HomeMy WebLinkAboutAPA3060VOLUME I
FEB 1 01986
RECEIVED
FINAL REPORT
DECEMBER 1985
DOCUMENT No.3060
N.J;,!,KA OffT.0"h,,)r1 60 GAME
SuitP River I8Ikl8lll flow
INSTREAM FLOW
RELATIONSHIPS REPORT
Alaska Power AU~hor;ty
Trihey&
Associates
Aquatic Resource
Specialists
CONTRACT TO
RZA-EErASCO
TNA JOINT VENTURE
FEDERAL ENERGY'REGULATORY COMMISSION
PROJECT No.7114
SUSITNA
HYDROELECTRIC PROJECT
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SUSITNA HYDROELECTRIC PROJECT
INSTREAM FLOW RELATIONSHIPS REPORT
VOLUME NO.1
Prepared by
Trihey and Associates
and
Entrix,Inc •
With assistance from
Document No.3060
Susitna File No.4.3.1.3
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Harza-Ebasco Susitna Joint Venture
R&M Consultants,Inc.
University of Alaska,
Arctic Environmental Information &Data Center
Woodward-Clyde Consultants,Inc.
Under contract to
Harza-Ebasco Susitna Joint Venture
Prepa red for
Alaska Power Authority ARLIS
Final Report
December 1985
Alaska Resources
Library &.InformatIOn ServIces
Anchorage.Ahu'llm
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NOTICE
ANY QUESTIONS OR COMMENTS CONCERNING
THIS REPORT SHOULD BE DIRECTED TO
THE ALASKA POWER AUTHORITY
SUSITNA PROJECT OFFICE
ARLIS·
Alaska Resources
Library &InfonnatlOn Services
Anchorage.Alaska
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ACKNOWLEDGMENTS
Preparation of the Instream Flow Relationship Report (IFRR)and its
associated technical report series was funded by the Alaska Power
Authority (APA)as part of the feasibility and licensing studies for
the proposed Susitna Hydroelectric Project.Much of the IFRRis based
on engineering and environmental studies which were initiated by Acres
Ameri can,Inc.and conti nued by Harza-Ebasco Susitna Joi nt Venture.
Except for the stream temperature modeling,Harza-Ebasco has conducted
all physical process modeling directly or indirectly referenced in
this document.Of particular value is their reservoir temperature and
instream ice modeling.
Field studies and analyses completed by other members of the Aquatic
Study Team are also cited within this report.Most visible are
numerous references to the Alaska Department of Fish and Game,Susitna
Hydroelectric Aquatic Study Team (ADF&G,Su Hydro).The ADF&G Su
Hydro Study Team conducted the baseline field studies to determine the
seasonal distribution,relative abundance,and habitat requirements of
anadromous and selected resi dent fi sh popul a ti ons withi n the project
area.
The University of Alaska,Arctic Environmental Information and Data
Center (AEIDC)performed the instream temperature modeling studies,a
key element in the evaluation of project influences on ice processes
and on the seasonal quality of fish habitats.Mr.Paul Meyer and
Mr.Joe Labelle are recognized for assembling the supporting technical
information and drafting portions of section IV of this report.
R&M Consultants conducted the hydrologic and climatologic field
studies for the project.Their greatest assistance has been in
providing data and technical assistance pertaining to basin hydrology
and climatology,slough geohydrology (upwelling),and ice processes.
Special recognition is given to Mr.Steve Bredthauer for drafting
portions of the basin hydrology and streamflow variability discussion
(section IV)and to Mr.Carl Schoch who provided technical information
and drafted porti ons of the i nstream temperature and ice processes
section .'
Finally,special recognition is given to Mr.Milo C.Bell for the
insights he provided at the onset of the feasibility and licensing
studies regarding the fish resource issues that would be of central
importance to project licensing and for his wise counsel concerning
the potentially beneficial and adverse influences the proposed project
may have on the salmon resources in the Susitna River Basin.
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-TABLE OF CONTENTS
ACI(r~OWLEDGMENTS II ..II ..II ........ .. .. .. .. .. .. .. .. .. ...... .. .. ..;
TAI3LE OF CONTENTS ....•-..iii
LI~5T OF FIGURES.........................................................................................vi
LI:5T OF TABLES -.........................................................x
I.INTRODUCTION..•.........•.•..........I-I
Instream Flow Relationships Report......................I-I
Project Setting........................................1-4
Susitna River Basin.~·.•..•............1-6
Overview of Fish Resources and Project-
Related Concerns ....•........•...............·1-7
II.OVERVIEW OF THE IFR ANALySIS...........................11-1
Overvi ew of Susitna Ri ver Fi sh Resources...............II I-I
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III.
Selection of Fish Habitat Over Fish
Populations for Decisionmaking .
Framework for Extrapolation:River
Segmentation,Habitat Types,and
Microhabitat Variables •...........................
FISH RESOURCES AND HABITAT TyPES ...............•...•..
Adult Salmon Contribution to Commercial
Fi shery '.
Sport fishing .
Subsistence Fishing .
Relative Abundance of Adult Salmon ...........•...•....•
Distribution and Timing of Juvenile Salmon
and Resident Species •....•........................
Juveni 1e Salmon .•.....••.•...•....•........•......
Resident Species .
Identification and Utilization of Habitat Types .•...•..
iii
II-I
II-3
II I-I
I II-I
III-4
II 1-5
111-8
III-12
111-12
III-12
I II-14
TABLE OF CONTENTS (Continued)
Mainstem Habitat ...'..........................•.•..
Side Channel Habitats .
Side Slough Habitats ..........•...................
Upland Slough Habitats ...........................•
Tributary Habitats ........•.......................
Tributary Mouth Habitat .
Selection of Evaluation Species ....•..•................
IV.WATERSHED CHARACTERISTICS AND PHYSICAL PROCESSES
INFLUENCING MIDDLE SUSITNA RIVER HABITATS .
I II-14
III-16
II 1-17
III-19
I II-20
I II-20
II 1-22
IV-I
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Watershed Characteristics..............................IV-I
Bas ina ve rv i ew .
Basin Hydrology .
Streamflow Variability and With-project
Operations .
Influence of Streamflow on Habitats .
IV-l
IV-l
IV-7
IV-12
Mainstem and Side Channel Habitats................IV-12
Side Slough Habitats..............................IV-12
Groundwater Upwelling and Intragravel Flow........IV-14
Biological Importance of Upwelling................IV-18
Sediment Transport Processes .IV-21
Influence of Sediment Transport Processes on Habitat
Types.. ... ... . . . . ... ... ...... . ... ... .... ... ...... ... ......... ......... IV-23
Instream Water Quality and Limnology...................IV-32
Baseline Condition................................IV-32
Mainstem and Large Side Channel Habitats .
Side Channel and Side Slough Habitats .
Tributary and Tributary Mouth Habitats .
Upland Slough Habitats •...........................
Project Influence on Sediment Transport Processes.
IV-23
IV-27
IV-28
IV-28
IV-29 -
Effects of Water Quality on Habitat Types..............IV-35
Mainstem and Side Channel Habitats .............•..
Side Slough Habitats .
Upland Slough Habitats .
Tributary and Tributary Mouth Habitats .
Wi th-Project Re 1a ti onshi ps .
iv
IV-35
IV-36
IV-38
IV-38
IV-41
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TABLE OF CONTENTS (Continued)
Instream Temperature and Ice Processes .
Temperature Criteria for Fish ......•..............
Instream Temperature Processes •...................
With-project Temperature Conditions .
Ice Processes .
Freez eu.p .
Breakup 41 .
Effects of With-Project Instream Temperatures on
Susitna Ri ver Ice Processes ...........•.....•
Effects of Ice Processes on Environmental
IV-46
IV-46
IV-48
IV-55
IV-61
IV-63
IV-67
IV-fi9
Conditions ·-IV-75
V.INFLUENCE OF STREAMFLOW AND INSTREAM HYDRAULICS ON
MIDDLE RIVER HABITATS ....•.•.•.........................V-I
Habitat Types and Transformation Categories............V-I
Microhabitat Repsonse to Instream Hydraulics...........V-9
Spawn.i ng Salmon .V-9
Rearing Salmon.........................................V-25
VI.S·UMMARY II..VI-l
VIr.
Influence of Streamflow on Habitat Types and
Other Variables .
Seasonal Utilization of Middle River Habitats .....
Evaluation Species and Periods ..............•.....
Relative Ranking and Physical Habitat Variables ...
Influence of Project Design and Operation on
Downstream Physical Processes and Fish Habitats ...
Sediment and Turbidity ........•.........•...•.....
Temperature and Ice Processes .
Streamflow II .
Fish Habitats II ••••••••
REFERENCES CITED .....................................•
v
VI-l
VI-3
VI-5
VI-7
VI-13
VI-14
VI-15
VI-16
VI-18
VII-l
Figure 1-1.
LI ST OF FI GURES
Project area ..1-8
Figure 11-1.Hierarchial structure of the relationship
analysis II C>..............................1I-7
Figure 11-2.Schematic diagram showing the integration of
physical processes and the habitat response
components of the Relationships Model .11-10
Figure III-I.General habitat types of the Susitna River
(ADF&G,Su Hydro 1983a)111-15
Figure 111-2.Relative distribution of salmon spawning
within different habitat types of the middle
Susitna River (Estes and Vincent-Lang 1984c)111-23
Figure 111-3.Relative abundance and distribution of
juvenile salmon within different habitat
types of the middle Susitna River (adapted
from Dugan et al.1984)111-26
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Fig ure I V-I.
Figure IV-2.
Figure IV-3.
Figure IV-4.
Figure IV-5.
Figure IV-5.
Fig ure IV-7.
Stream network within the Susitna River Basin .
Average monthly air temperatures (OC)in the
upper and lower basins of the Susitna River
(R&M 1984a,1985a;U.S.Dept.of Commerce
1983,1984)1Ill 4I4I ..
Estimated percent contributions to middle
Susitna River streamflow .......................•.......
Naturally occurring annual peak flows,mean
summer di scharge,and annual streamflow of
the Susitna River at Gold Creek (adapted from
Harza-Ebasco 1985c as modified by AEIDC
1985b)011 ..
Estimated with-project mean monthly flows at
Gold Creek compared to natural flows (adapted
from APA 1985b)...........•.....•......................
Cross sections of the Susitna River at Gold
Creek measured at various mainstem discharges .
Empirical relationship of naturally occurring
turbi dity versus suspended sediment concen-
tration for rivers in Alaska,sampled during
May -October,1976-1983 (Lloyd 1985,derived
from data provided by USGS).........................•..
vi
IV-2
IV-3
IV-6
IV-8
IV-9
IV-24
IV-43
Figure IV-8.
Figure IV-9.
Theoretical curve of turbidity versus compen-
sation depth (Reub et al.1985).....................•..
Chum salmon spawning time versus mean incu-
bation temperature nomograph (Univ.of
Alaska,AEIDC 1985a)•.•.•.•.•.•.......•......•.....•...
IV-42
IV-50
Figure IV-10.Comparison between average weekly stream
temperatures for the Susitna River and its
tributaries (adapted from Univ.of Alaska,
AEIDC 1985a)..
Figure IV-II.Generalized flowchart of ice formation
processes within the middle reach of the
Susitna River •..................•..•..•................
Figure IV-12.Duration of the ice-covered period and
maximum upstream extent of ice cover on the
mi ddl e Susitna Ri ver under natural and
with-project conditions (adapted from
Harza-Ebasco 1985d).
Figure V-I.Surface area response to mainstem discharge
in the Talkeetna-to-Devil Canyon reach of the
Susitna River (RM 101 to 149).......•..................
IV-52
IV-62
IV-72
V-2
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Figure V-2.
Figure V-3.
Figure V-4.
Figure V-5.
Fi gure V-6.
Fiigure V-7.
Flow chart classifying the transformation of
middle Susitna River aquatic habitat types
between two flows (Habitat Transformation
Cate-gori·es 0-10)..
Number of specific areas classified in each
habitat category for various Gold Creek
rna ins t em dis cha r'g es .. ..•.. .. .......... .. .. .. .. ..til .... .. .. .. .. .. .. .. .. .. .. .. ...... .. .. .. ..
Habitat suitability criteria for slough
spawning chum and sockeye salmon (Estes and
Vi ncent-Lang 1984d).............................•.•.•..
Comparison of WUA responses to site flow for
spawning chum and sockeye salmon at four
middle Susitna River study sites (adapted
from Estes and Vincent-Lang 1984d)....•................
Total surface area and WUA index for spawning
chum salmon at Habitat Category I,II,and
III study sites (adapted from Estes and
Vincent-Lang 1984d)................................•...
Simulated influence of increased upwelling on
WUA for spawning chum salmon at Slough 21 and
Upper Side Channel 11 ..................•.•.............
vii
V-5
V-7
V-l1
V-IS
V-17
V-18
Figure V-So
Figure V-g.
Surface a rea and WUA responses to rna i nstem
discharge at Habitat Category I,II,and III
spawni n9 sites {adapted from Estes and
Vincent-Lang 19S4a).......•..•...••...•.•.••...........
Frequency distribution of cell depth over
upwelling areas in Upper Side Channel 11 at
site flows of 5 and 50 cfs •............................
V-19
V-21
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Figure V-10.Frequency distribution of cell velocity over
upwelling areas in Upper Side Channel 11 at
site flows of 5 and 50 cfs ........•....................
Figure V-I!.Flow and habitat duration curves for spawning
chum salmon by habi tat categori es ............•.•.....•.
Figure V-12.Velocity criteria for juvenile chinook in
clear and turbid water ..............•.....•............
Figure V-13.ADF&G cover criteria for juvenile chinook in
clear and turbid water conditions .
Figure V-14.Velocity suitabil ity criteria for juvenile
chinook in the Kenai and Chakachamna rivers,
Alaska {Burger et al.1982 and Bechtel Civil
and Minera 15 1983).
V-22
V-23
V-27
V-28
V-29
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Figure V-15.Velocity suitabil ity criteria used to model
juvenile chinook habitat (WUA)under clear
and turbid water conditions in the middle
Susitna River (Steward 1985)...........................V-31
Figure V-16.Revised cover criteria for juvenile chinook
in clear and turbid water..............................V-35
Figure V-17.Comparison between WUA forecasts using ADF&G
low turbidity velocity criteria (solid line)
and modified low turbidity velocity criteria
(dashed line)..........................................V-36
Figure V-lB.
Figure V-19.
Figure V-20.
Comparison between WUA forecasts using ADF&G
(solid line)and modified cover criteria
(dashed line)for juvenile chinook .
Si rnul ated effect of reduci ng fi ne sediment
deposition at two study sites .
Comparison between WUA forecasts using ADF&G
and revised rearing habitat model~.
viii
V-37
V-39
V-40
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Figure V-21.Percent of total wetted surface area provid-
ing WUA for rearing chinook at Side Channel
21 and Upper Side Channel 11 .
Figure VI-I.Phenology and habitat utilization of middle
Sus itna Ri ver salmon in rna i nstem,tributa ry,
and slough habitats (adapted from Woodward-
Clyde and Entrix 1985)...........•.......•.............
Figure VI-2.Ranking of habitat component in accord with
the degree of control project design and
operation might provide them ........................•..
ix
V-42
VI-6
VI-I?
LIST OF TABLES
Table III-I.Common and scientific names of fish species
recorded from the Susitna River basin (from
Alaska Dept.of Fish and Game,Susitna Hydro
Aquatic Studies).
Table 1II-2.Commercial catch of upper Cook Inlet salmon
in numbers of fish by species,1954-1984
(from Alaska Dept.of Fish and Game,Commer-
cial Fisheries Div.,Anchorage,AK)...•.•.•............
Table III-3.Summary of commercial and sport harvest on
Sus itna Ri ver ba sin adu It sa 1man retu rns .
Table III-4.Sport fish harvest for Southcentral Alaska
and Susitna Basin in number of fish by
species,1978-1983 (from Mills 1979,1980,
1981,1982,1983,1984).
Table 111-5.Average salmon escapements in the Susitna
River by species and location (from Barrett
eta 1.1984,1985).....................................
II 1-2
II 1-3
111-6
1II-7
II 1-9
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Table IV-I.
Table IV-2-.
Table IV-3.
Table IV-4.
Table IV-5.
Table IV-6.
Summary of monthly streamflow statistics for
the Susitna River at Gold Creek from 1949 to
1982 (from Harza-Ebasco 1984g).
Percent distribution of annual peak flow
events for the Sus i tna Ri ver at Gold Creek
1950-1982 (R&M Consultants 1981b).
Flood peak frequency data at Go 1d Creek for
natura 1 and with-project conditi ons (Harza-
Ebasco 19S5c)ill ..
Number of times during the spawning period
mainstem discharge was equal to or greater
than the breach i ng flow for the consecutive
number of days and years indicated .
Influence of mainstem sediment load,on
streambed composition of aquatic habitat
types ..
Influence of sediment transport processes on
streambed stability of aquatic habitat types .
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IV-4
IV-7
IV-lO
IV-15
IV-23
IV-25
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-Table IV-7.
Table IV-8.
Mean baseline water quality characteristics
for middle Susitna River at Gold Creek under
(a)turbid summer (June -August)conditions
and (b)clear!winter (November -April)
conditi ons (from Al aska Power Authority
1983b).... .. .. .. .. .. .. ......... .. .. .. .. .. .. .. .. ...... .. .. .. .. .. .. .. .. .. .. .. .. ...... .. .. .. .. .. .. .. .. .. ..IV-34
Difference in compensation depths calculated
from with-project suspended sediment concen-
trations (mg/l)using two different relation-
ships between turbidity (NTU)and TSS .........•.........IV-44
Table VI-9.Preliminary stream temperature criteria for
Pacific salmon developed from literature
sources for application to the Susitna River
(University of Alaska!AEIDC 1984).IV-47
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Table IV-10.Comparison of accumulated centigrade tempera-
ture units (CTU)needed to produce 50 percent
hatching of chum salmon eggs and 50 percent
emergence of chum salmon alevins at selected
sites on the Susitna River with those
required under controlled incubating environ-
ments elsewhere in Alaska .•••..•.......•.....•........•IV-49
-Table IV-l1.
Table IV-12.
Comparison between measured surface water
temperatures (0C)in side sloughs and sim-
ulated mainstem temperatures (from ADF&G!Su
Hydro 1983b,1983c).•...•...............•.....•.•......·IV-54
Downstream temperatures (OC)resulting from
differences in summer reservoir release flows
and temperatures.............................................................................IV-57
Table IV-13.
Table IV-14.
Table IV-IS.
Table IV-16.
Downstream temperatures (OC)resulting from
differences in winter reservoir release flows
and tempe r'a tu res ..
Comparison between simulated downstream water
temperatures for constant reservoi r outflow
conditions and different air temperatures .
Summary of freeze up observations for several
locations within the Talkeetna-to-Devil
Canyon reach of the Susitna River.(R&M
Consultants 1981a!1982b,1983a!1984b).
Occurrences where with-project maximum river
stages are higher than natural conditions
(Harza-Ebasco Susitna Joint Venture 1984c).
xi
IV-58
IV-59
IV-65
IV-74
Relative degrees of influence that habitat
variables exert on the suitability of middle
Susitna River habitat types during the four
evaluation periods.....................................VI-8
Table V-I.
Table V-2.
Table V-3.
Table V-4.
Tab 1e VI-I.
Table VI-2.
Description of habitat transformation cat-
egorl es ..
Mean column velocity measurements (fps)
collected at chum salmon redds in several
rivers of Washington state {Johnson et al.
1971)C1 ••II
Calculation of turbidity factors for deter-
mination of the infl uence of turbidity on
clear water cover criteria for juvenile
chinook salmon (Suchanek et al.1984)....•.............
Habitat suitabi 1 ity criteria used in revi sed
model to forecast WUA for juvenile chinook
salmon under low and high turbidities .
Evaluation periods as defined by water weeks .
V-4
V-13
V-33
V-4I
VI-5
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Table VI-3.
Table VI-4.
Table VI-5.
Summary of habitat and evaluation period
indices for the middle Susitna River as
derived in Table VI-2..................................VI-II
Relative degrees of influence that estimated
with-project physical habitat variables might
have on the suitability of middle Susitna
River habitat types during the four eval-
uation periods.........................................VI-19
Comparison between habitat and evaluation
period indices for natural (N)and with-
project (P)conditions.................................VI-20
xii
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I.INTRODUCTION
Instream Flow Relationships Report
The goal of the Alaska Power Authority in identifying environmentally
acceptable flow regimes for the proposed Susitna Hydroelectric Project
is the maintenance of existing fish resources and levels of produc-
tion.This goal is consistent with the preferred mitigation goal of
the U.S.Fish and Wildlife Service and the Alaska Department of Fish
and Game which encourages the maintenance of naturally occurring fish
habitats and populations.
In 1982,following two years of baseline studies,a multi-disciplinary
approach to quantify effects of the proposed Susitna Hydroe 1ectri c
PY'oject on existing fish habitats and to identify mitigation oppor-
tuniti es associ ated with streamflow and/or stream temperature regu-
lations was initiated by the Power Authority.The Instream Flow
Relationships (IFR)studies were initiated to identify the potential
beneficial and adverse effects the proposed Susitna Hydroelectric
PY'oject might have on fluvial processes and fish habitat in.the
Talkeetna-to-Devil Canyon segment of the Susitna River (middle Susitna
River).The IFR studies focus on quantifying the response of fish
habitats in the middle Susitna River to incremental changes in
mainstem discharge,temperature,and water quality.As part of this
multi-disciplinary effort,a technical report series was planned that
would (1)describe the existing fish resources of the Susitna River
and identify the seasonal habitat requirements of selected species,
and (2)evaluate the effects of alternative project designs and
operating scenarios on physical processes which most influence the
seasonal availability of fish habitat.
In addition,a summary report,the Instream Flow Relationships Report
(IFRR),would (1)identify the biologic significance of the physical
processes evaluated in the technical report series,(2)integrate the
findings of the technical report series,and (3)provide quantitative
relationships and discussions regarding the influences of incremental
I-I
changes in streamflow,stream temperature,and water quality on fish
habitats in the middle Susitna River.By meeting these objectives the
IFR studies will assist the Alaska Power Authority (APA)and resource
agencies to reach an agreement on an instream flow regime (and
.associated mitigation plan)that would minimize adverse effects of the
proposed project and possibly enhance existing fish habitats and
populations in the middle Susitna River.
The IFRR consists of two volumes.Volume I uses project reports,data
and profess i ona 1 judgement to identify eva 1uati on speci es,important
life stages,and habitats.The report also ranks a variety of
physical habitat variables with regard to their degree of influence of
fish habitat at different times of the year.This ranking considers
the biologic requirements of the evaluation species and life stage,as
well as the physical characteristics of different habitat types,under
both natural and anticipated with-project conditions.Volume II of
the IFRR,which will be completed during 1986,will provide a
quantitative framework and the necessary relationships to evaluate
influences of incremental changes in streamflow,stream temperature
\
and water quality on fish habitats in the middle Susitna River on a
seasonal basis.
The technical reports which support the IFR Volume I consist of the
four reports listed in Table I-I as well as several reports prepared
by the Alaska Department of Fish and Game,Su Hydro Aquatic Studies
Group which describe fish habitats,populations and utilization
patterns,and reports by the Harza-Ebasco Susitna Joint Venture which
address reservoi r temperature,i nstream ice processes,groundwater
hydrology,and sediment transport.
Table I-I IFR Studies Technical Report Series
Technical Report No.1.Fish Resources and Habitats in the middle
Susitna River.This report prepared by Woodward-Clyde Consultants and
Entrix,Inc.consolidates information obtained by ADF&G,Su Hydro on
1-2
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the fish resources and habitats in the middle Susitna River and
summarizes the relative abundance and seasonal uti1 ization patterns
observed in middle Susitna River habitats from 1981 through January
1985.
Technical Report No.2.Physical Processes of the Middle Susitna
Rjiver.This report,prepared by Harza-Ebasco and R&M Consultants,
describes such naturally occurring physical processes within the
mojddle river segment as:sediment transport,channel stability,ice
cover formation and upwelling.
Technical Report No.3.A Limnological Perspective of Potential Water
Quality Changes.This report,prepared by Harza-Ebasco,consolidates
existing information on the water quality for the Susitna River and
prOVides technical level discussions of the potential for with-project
b'i oaccumul ati on of mercury,nitrogen gas supersaturati on and changes
in downstream nutrients.Particular attention is given to project
induced changes in turbidity and suspended sediments concentrations.
TI=chnical Report No.4.Instream Temperature.This report,prepared
by the University of Alaska Arctic Environmental and Data Center,
consists of three principal components:(1)instream temperature
modeling;(2)development of temperature criteria for Susitna River
fish stocks by species and life stage;and (3)a preliminary eval-
uation of the influences of anticipated with-project stream tempera-
tures on fish habitats and ice processes.
The IFR report and its associated technical report series should not
bt=viewed as an impact assessment.These reports only describe a
vi3.riety of natural and with-project conditions that govern,or may
govern,fluvial processes and the seasonal availability and quality of
fish habitat in the middle Susitna River.The IFR studies provide the
quantitative basis for others to evaluate alternative streamflow and
stream temperature regimes,conduct impact analyses,and prepare
mitigation plans.Brief descriptions of anticipated with-project
conditions are provided in Section VI of this report.However,these
descriptions only serve to establish a basis for understanding the
riel ati ve importance of anti ci pated with-project habitat conditions
with regard to the life history requirements of the evaluation
speci es.Quantitative descri ptions or di scussi ons of project effects
on fish habitat,as expected in an impact assessment,are not provided
by this report.
1-3
Project Setting
The proposed Susitna Hydroelectric project consists of two dams
scheduled for construction over a period of 21 years.The three-stage
project would be initiated by construction of Watana Dam to a crest
elevation of 2,025 feet with a maximum reservoir elevation of 2,000
feet.Construction on Watana Dam would begin when the FERC license is
issued,possibly in 1987,and would occur at a site located approxi-
mately 184 miles upstream from the mouth of the Susitna River.The
first stage of the Watana development would be completed in 1996 and
would include a 70S-foot-high earth fill dam,which would impound an
approximately 21,OOO-surface-acre reservoir with 2.37 million acre
feet (maf)of usable storage.Cone valves and multiple level intake
structures would be installed in the dam to control downstream dis-
solved gas concentrations and temperature.The powerhouse would
contain four generators with an installed capacity of 520 megawatts
(MW)and would be designed to discharge a 50-year flood before flow
would be discharged over the spillway.
The second stage of the proposed development is construction of the
646-foot-high concrete ~rch Devil Canyon Dam,which is scheduled for
completion by 2002.Devil Canyon Darn would be constructed at a site
32 miles downstream of Watana Dam and would impound a 26-mile-long
reservoi r wi th 7,800 surface acres and a usable storage capacity of
0.35 maf.Installed generating capacity would be about 600 MW,with
an average annual energy output of 3450 gigawatt hours (GWH).Cone
valves and multiple level intake structures would also be installed in
Devil Canyon Dam.The maximum possible outflow from the four genera-
tors in the powerhouse at full pool is 15,000 cubic feet per second
(cfs).The cone valves at Devil Canyon Dam would be designed to pass
38,500 cfs.Prior to construction of Devil Canyon Dam,Watana Reser-
voir would be filled with summer streamflows when energy demand is
lowest and would be drawn down to meet high power demands during the
winter when streamflows are lowest.When Devil Canyon Dam became
operational,Hatana Reservoir would operate in a similar manner,
however,the level of winter drawdowns may not be as low.Devil
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-Canyon Reservoir water levels would generally be stable with a small
drawdown in the spring of dry years and a larger drawdown in the fall
of average and dry years.
The third stage of the project consists of ralslng the initial crest
elevation of Watana Dam from 2,025 feet to 2,205 feet with a maximum
normal reservoir elevation of 2,185 feet.Completion of the third
stage is scheduled for the year 2008.When completed,Watana Dam
~Iould be 885 feet high and would impound a 48-mile-long,38,000-
surface-acre reservoir with a total storage capacity of 9.5 maf and a
usable storage capacity of 3.7 maf.Two additional generators would
be added to the powerhouse,bringing the total number to six units.
Plfter completion of Stage III,the capacity of the powerhouse would
increase to 1,020 MW because of the increased head on the four Stage I
units and the addition of two more units at 170 MW each.The maximum
powerhouse discharge capacity at full pool would be greater than
21,000 cfs (APA 1983).Watana Reservoir,because of its size,would
provide the abil ity to completely rE79ulate Susitna River streamflows
except during extreme flood events.
1-5
Susitna River Basin
The Susitna River is located in Southcentral Alaska between the major
population centers of Anchorage and Fairbanks.The Susitna Valley is
a transportation corridor which contains both the Alaska Railroad and
the Parks Hi ghway.Even wi th these transportati on facil ities,how-
ever,the basin remains largely undeveloped except for several small
communities in the lower portion of the drainage.Talkeetna,the
largest of these communities,with an approximate population of 280,
is located on the east bank of the Susitna River at river mile
(RM)98.1
The Susitna River is an unregulated glacial river.Typical summer
flows range from 16,000 to 30 ,000 cfs wi th wi nter flows rang"j ng
between 1,000 and 3,000 cfs.Turbidities in the middle Susitna River
average approximately 200 nephelometric turbidity units (NTU)in
summer,and less than 10 NTU in winter.Summer flows are quite
variable,often changing from 5,000 to 10,000 cfs from one week to the
next;peak flows exceeding 50,000 cfs are common.Winter streamflows
are maintained principally by groundwater and therefore are quite
stable.A thick ice cover generally forms on the river during late
November and persists through mid-May.
The drainage area of the Susitna River,the sixth largest river basin
in Alaska,is approximately 19,600 square miles.The Susitna Basin is
bordered by the Alaska Range to the north,the Chulitna and Talkeetna
mountains to the west and south,and the northern Talkeetna plateau
and Gul kana upl ands to the east.Major tributaries to the Susitna
include the Talkeetna,Chulitna,and Yentna Rivers,all of which are
glacial streams with characteristically high turbid summer streamflows
and ice-covered clearwater winter flows.
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1 River miles are measured upstream from the mouth of the Susitna
River which is located in Cook Inlet approximately 25 miles
northwest of Anchorage.
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The Yentna River,the largest tributary to the SlJsitna River
originates at the Dall and Yentna glaciers in the Alaska Range
approximately 130 miles northwest of Anchorage and adjoins the Susitna
R<iver at RM 28.The Chulitna River originates in the glaciers on the
south slope of Mount McKinley and flows south,entering the Susitna
River near Talkeetna at RM 99.The Talkeetna River originates in the
Talkeetna Mountains,flows west,and joins the Susitna near the town
of Talkeetna (RM 97).The junction of the Susitna,Chulitna and
Talkeetna Rivers is commonly referred to as the Three Rivers
confl uence.
The Susitna River originates as a number of small tributaries draining
the East Fork,Susitna,West Fork and MacLaren Glaciers,and follows a
disjunct south and west course 320 miles to Cook Inlet (Fig.I-I).
The river flows south from these glaciers in a braided channel across
a broad alluvial fan for approximately 50 miles,then west in a single
channel for the next 75 miles through the steep-walled Vee and Devil
Canyons.The two proposed dam sites (Watana at RM 184.4 and Devil
Canyon at RM 151.6)are located in this reach.Downstream of Devil
Canyon,the ri ver flows south again through a we ll-defi ned and re 1a-
tively stable multiple channel until it meets the Chulitna and
Talkeetna Rivers (RM 99).Downstream of the Three Rivers confluence,
the Susitna River valley broadens into a large coastal lowland.In
this reach the down valley gradient of the river decreases and it
flows through a heavily braided segment for the last 100 miles to the
estuary.
Overview of Fish Resources and Project-Related Concerns
The Susitna River basin supports popul ations of both anadromous and
resi dent fi sh.Commerci alar sport fi sheri es exi st for fi ve speci es
.of Pacific salmon (chinook,sockeye,coho,chum,and pink),rainbow
trout,lake trout,Arctic grayling,Dolly Varden,and burbot.The
commercial fishery intercepts returning sockeye,chum,coho and pink
salmon in Cook Inlet.A subsistence fishery at Tyonek relies princi-
pally on chinook salmon.Sport fishing is concentrated in clearwater
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COOK INLET
[7 <.uu:ANCHORAGE
+10 Rivermilt Incremenls
Scale'I'"16mil ..
Fi gure 1-1.Project area.
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tributaries to the Susitna River for chinook,coho,and pink salmon;
rainbow trout;and Arctic grayling.These fish resources are
described further in Section III of this report.
Construction and operation of the proposed project will reduce varia-
tion in the annual flow cycle by decreasing streamflows during the
summer months and increasing them during the winter months.Stream
temperatures and turbidities will be similarly affected.The most
pronounced changes in stream temperature and turbi dity wi 11 1i kely
occur in mainstem and side channel areas with somewhat lesser effects
occurring in peripheral habitats.Changes in depth and velocity
attributable to alteration of natural streamflow patterns will be most
pronounced and of greatest concern in peri phera 1 areas;pa rti cul arly
if extensive or untimely dewatering or flooding of fish habitat might
occur.
The effects that anti ci pated changes in streamflow,stream tempera-
ture,and turbidity will have on fish populations inhabiting the
mi ddl e Susitna Ri ver depend upon thei r seasonal habitat requi rements
and the importance of the requirements to the overall population.Some
project-induced changes in environmental conditions may have no
appreciable effect on existing fish populations and their associated
habitats,whereas other changes may have dramatic consequences.Thus,
in order to understand the possible effects of the proposed project on
exi sti ng fi sh popul ati ons and to identify miti gati on opportuniti es or
enhancement potential,it is important to understand 1)the relation-
ships among the naturally occurring physical processes which provide
fish habitat,and 2)how fish populations respond to natural variations
in habitat availability.
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II.OVERVIEW OF THE IFR ANALYSIS
Selection of Fish Habitat Over
Fish Populations for Decisionmaking
Identification of an environmentally acceptable flow regime to main-
tain naturally reproducing fish populations has remained of central
importance throughout the evolution of the studies for the proposed
Susitna project.In describing the potential effects of the proposed
project the IFR studies have focused on identifying the response of
fluvial processes and fish habitats to incremental changes in mainstem
discharge,temperature,and water quality.This approach is consis-
tent with the mitigation goals of the Alaska Power Authority,U.S .
Fish and Wildlife Service,and the Alaska Department of Fish and Game
(USFWS 1981;ADF&G 1982;APA 1982).The ultimate goal of these
organizations'mitigation policies is the maintenance of natural
habitats and production levels.
Fish populations of the Susitna River are thought to fluctuate for
many reasons,with some of the factors exerti ng their i nfl uence
outside the river basin.This is particularly true for anadromous
species such as Pacific salmon,which spend substantial portions of
their life cycles in estuarine.and marine environments.Ocean
survi va 1 and commerci a1 catches si gnifi cantly affect the number of
salmon returning to spawn in the Susitna River basin (ADF&G 1985).
Withi n the freshwater envi ronment,factors such as hi gh flows and
suspended sediment concentrations during summer,cold stream tempera-
tures,low winter streamflows,predation,and sport fishing appear to
affect populations.
Furthermore,adult fi sh popul ati ons seldom show an immedi ate response
to perturbati ons that may occur ei ther withi n or outsi de thei r
freshwater envi ronment.A time-l ag,often of several years ,usually
occurs before an effect,whether beneficial or detrimental,is
reflected in the reproductive potential or size of the population.
II-I
For these reasons it is often impossible to forecast the response of
fi sh popul ations to project-i nduced changes in fl uvi a"processes by
monitoring fish populations only.
To avoid many of the uncertainties associated with correlating fish
population levels with various environmental parameters,fish habitat
is often used as a response va ri ab 1e in determi ni ng the effects of
altered fluvial processes on fish populations (Stalnaker and Arnette
1976;Olsen 1979;Trihey 1979).The application of physical process
modeling is well suited for obtaining reliable forecasts of with-
project streamflow,temperature,and water quality conditions which,
in turn,can be readily interpreted in terms of habitat suitability.
When using fish habitat as the response variable,the direction and
magnitude of change 'in habitat availability or habitat quality are
considered indicative of the population response.Although the
relationship between habitat availability or quality and fish
population is not necessarily linear,it has been found to be
positively correlated in several studies (Binns and Eiserman 1979;
Wesche 1980;Loar et al.1985).
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Framework for Extrapolation:
River Segmentation,Habitat Types,and Microhabitat Variables
Various approaches exist for evaluating fish habitats associated with
fluvial systems.Weighted Usable Area (WUA)is often used at the
microhabitat level as an index to evaluate the influence of streamflow
variations on the site-specific avai1ability of potential fish habi-
tat.Weighted Usable Area is defined as the total wetted surface area
of a study site expressed as an equivalent surface area of optimal
(preferred)fish habitat for the life species and stage being evalu-
ated (Stalnaker 1978).This index is most commonly computed using
microhabitat variables such as depth,velocity,and substrate composi-
tion for spawning fish,and depth,velocity,and cover for rearing
fish.Occasionaly stream temperature is also included.WUA forecasts
for habitats in the middle Susitna River are enhanced by considering
such other microhabitat variables as upwelling groundwater and
turbi dity.
The microhabitat approach can effectively evaluate habitat suitability
in terms of physical conditions occurring at specific locations
(areas)within a river system.However,in order to evaluate aquatic
habitat responses to physical processes on a larger scale,some method
must be established for extrapolating site specific relationships to
the remainder of the river.
The representative reach concept (Bovee andMi -I hous 1978 )is often
Ulsed by instream flow investigators as a basis for extrapolating.
This concept is based on the theory of longitudinal succession which
describes riverine ecology and fluvial processes from the headwaters
to the mouth of a river (Burton and Odum 1945;Mackin 1948;Sheldon
1968).Watershed characteristics such as climate,hydrology,geology,
topography,and vegetative cover (land use)are the principal determi-
nants of basin runoff and erosional processes which control longitudi-
na 1 successi on.By applyi ng the 1ongitudi na 1 success i on approach to
the existing river system and by considering differences project
II-3
operation would have on the type and magnitude of change in fluvial
processes within various river segments,the 320-mile length of
the Susitna River was divided into the four discrete segments.
1.Upper Basin (RM 232-320).This segment includes the headwater
reach of the Susitna River and its associated glaciers and
tributary streams above the elevation of the proposed impound-
ments.
2.The Impoundment Zone (RM 150-232).Thi s segment i ncl udes the
SO-mile portion of the Susitna River which will be inundated by
the Wataria and Devil Canyon impoundments.Thi s si ngle channel
reach is characterized by steep gradients and high velocities.
Intermittent islands are found in the reach with significant
rapids occurring in Vee Canyon and between Devil Creek and Devil
Canyon.
3.The Middle River (RM 99-150).This 50-mile segment (the focus of
the IFRR)extends from Devil Canyon downstream to the Tal keetna
and Chulitna Rivers confluence.It is a relatively stable reach
comprised of nearly equal lengths of single channel and spl it
channel characteristics.Construction and operation of the
project will alter the quantity and temperature of streamflow and
the amount of suspended and bedload sediment in this reach.
4.The Lower River (RM 0-99).Thi s segment extends 100 mil es from
the three rivers confluence downstream to the estuary.The
floodplain is very broad,containing multiple or braided channels
which meander laterally.Reworking of streambed gravels in this
area is relatively frequent causing instability and migration of
the main flow channel or channels.Project induced changes in
streamflow,stream temperature,and sediment concentrations will
attenuate in this reach due to tributaries such as the Talkeetna,
Chulitna,and Yentna Rivers,all of which will be unaffected by
project operation.
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Extrapolation of microhabitat responses in fish habitat to non-modeled
portions of the river using the traditional concepts of longitudinal
sJUccession is accomplished by dividing the river into segments of
similar channel morphology,water quality or species composition.
Likewise,the segments are further subdivided into subsegments of
similar hydraulic,hydrologic,and morphologic characteristics.
Subsegments are then defined according to habitat type by measurements
obtained in representative reaches.Systemwide habitat evaluation is
accomplished by extrapolating habitat relationships for representative
reaches to the subsegments and segments in which they are located on
the basis of proportional length.
The longitudinal succession approach is most applicable to single-
thread river systems in which subsegments containing relatively
homogeneous habitat types can be identified.In multi-thread systems,
such as the Susitna River,the longitudinal succession approach is
difficult to apply because the locations of homogeneous habitat types
are highly variable,both longitudinally and laterally within the
river corridor.Although the Susitna River can be divided into the
four discrete segments previously described,subdividing the middle
Susitna River segment into subsegments by application of the
representative reach concept (Bovee and Milhous 1978)does not provide
a practical method of extrapolating site specific relationships to the
remainder of the river.Hence,a different method for extrapolating
aquati c habitat responses to streamflow is requi red at th is 1eve 1 in
the hierarchy of the IFR analysis.
Because of the notable variation and differences in habitat conditions
within the middle Susitna River segment,six major habitat types have
been defined:mainstem,side channel,side slough,upland slough,
tributary,and tributary mouth (ADF&G,Su Hydro 1983a;Klinger &
Tri hey 1984).Habitat type refers to a major portion of the wetted
surface area of the river possessing similar morphologic,hydrologic,
and hydraulic characteristics.At some locations,such as major side
channels and tributary mouths,a designated habitat type persists over
a wide range of mainstem discharge even though the wetted surface area
II-5
for the location may change significantly.In other instances the
habitat type and wetted surface area may change in response to
mainstem discharge (Klinger and Trihey 1984).Such an example is the
transformation of some turbid-water side channels to clearwater side
sloughs when mainstem discharge recedes during late summer and fall.
Habitat transformation categories are used in the IFR analysis to
classify specific areas within the river corridor according to the
nature of the habitat transformation they undergo as mainstem dis-
charge decreases below typical mid-summer flow levels.The classi-
fi cati on of specifi c areas into habitat dewatered or transformation
categories is important because (1)a significant amount of wetted
surface area is expected to be transformed from turbid to clear water
habitats as a result of project-induced changes in streamflow (Klinger
and Trihey 1984);and (2)a large amount of circumstantial evidence
exists within the project data base and elsewhere which indicates that
turbid water channels which may be transformed into clearwater habi-
tats as a result of the project may provide substantially different
habitat conditi ons than presently exi sts in these channel s.Withi n
the hierarchial structure of the IFR analysis,the eleven habitat
transformation categories introduced in Section V provide important
indices of site-specific habitat response to large changes in mainstem
discharge.
Habitat transformation categories are used in conjunction with hydro-
logic,hydraul ic,and morphological information to group specific
areas of the middle Susitna River into representative groups.These
groups provide a basis to 1 ink microhabitat study sites (modeled
sites)with less intensively studied specific areas (nonmodeled
sites).Representative groups provide the analytic bridge to extrapo-
late habitat response functions from modeled to nonmodeled sites.
Figure II-I diagrams the hierarchial structure of the IFR analysis,
proceeding from microhabitat study sites through representative groups
and habitat types to the middle Susitna River segment.This analytic
structure is similar to the study site and representative reach logic
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Middle River Segment
/\
1.--
I 6 Habitat Types I
i\
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II Representative Groups
-and
Habttat Transformation
Categories
35 Study Sites
Figure.II-l.Hierarchial structure of the relationship analysis.
II-7
referenced in the literature and other instream flow studies (Bovee
and Milhous 1978;Wilson et ale 1981;Bovee 1982).
However,a basic difference exists between the structure of the
extrapolation methodology used in th IFR studies and that used in
other instream flow studies.In the IFR extrapolation methodology
habitat types and representative groups are substituted for river
subsegments and representati ve reaches.Additi ona l1y,the IFR
methodology uses wetted surface area rather than reach length as the
common denominator for extrapolation.Given the spatial diversity and
temporal variation of riverine habitat conditions within the middle
Susitna River the hierarchial structure of this analysis is considered
more applicable than routine adherence to extrapolation methodologies
based on longitudinal succession and the representative reach concept.
Sufficient data is available to identify the seasonal and microhabitat
reql..lirements of resident fish,and of adult and juven"ile salmon
indigenous to the middle Susitna River (ADF&G,Su Hydro 1983d;Estes
and Vincent-Lang 1984d;Schmidt et al.1984).Physical process models
have been developed to evaluate stream temperature,ice cover,
sediment transport,and site specific hydraulic conditions for a broad
range of streamflow and meteorologic conditions (Peratrovich et al.
1982;Univ.of Alaska,AEIDC 1983;Estes and Vincent-Lang 1984d;
Harza-Ebasco 1984b;Ha rza-Ebasco 1984e;Hill i ard et a 1.1985).The
surface area response of aquatic habitat types to mainstem discharge
has been estimated (Klinger and Trihey 1984;Klinger-Kingsley 1985),
and 172 modeled and non-modeled sites have been classified into ten
representative groups (Aaserude et ale 1985).These data bases are
sufficient to quantitatively model habitat response to alternative
streamflow and stream temperature regimes at both the microhabitat and
habitat levels.Finally,knowledge of the influences of mainstem
discharge on groundwater upwelling and water quality is sufficient to
be incorporated into this analysis in a structured,but subjective
manner.
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At present,the numerous components and linkages of a habitat response
model for the middle Susitna River remain at various stages of
dl:velopment.However,enough progress has been made to subjectively
evaluate the data base and provide various forecasts of streamflow-
dl:pendent habitat relationships.To this end,Section III describes
the fish resources and habitat types of the middle Susitna River and
identifies the evaluation periods and the primary and secondary
evaluation species;Section IV discusses the principal watershed
characteristics and physical processes which influence the seasonal
availability and quality of fish habitat;and Section V describes the
influence of streamflow and instream hydraulics on the availability of
habitat types and quality of microhabitat conditions.Section VI
summarizes the major conclusions which can be obtained from a subjec-
tive application of the IFR model (Fig.II-2)using the information
presented in sections IV and V.Section VI also describes the
relative importance of several physical processes and habitat
variables with regard to the primary evaluation species identified in
Secti on II 1.Anti ci pated with-project changes to natural processes
and relationships are discussed in general terms to introduce the
reader to several differences between existing and with-project
fluvial processes that will be important to consider in future
analyses.A more detailed discussion of the relationships between
physical processes and habitat response will be provided in Volume II
of the IFRR.
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I PHYSICAL PROCESS I
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OE Eatl",at..:!w.....IIQualityF'<N'.....t ...I
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HABITAT
RESPONSE
Ilvallallle .......(byISIIr1_.......~Are<l Ilt Spec 111 c ~IIQbitot type)NotIl.epone.~f I.GccItIoft _
Limited by T..."......,..
bl'Habitat Typ.O!'Wat..Quollfy Duri"ll
S<toeon 8pecffi.d
C«rcbor aft.."".Id Co",paette H_
I HABliJ(TRECCIfj ~Habitat In<It........d I"dle..b)'......-rtv.Sit.CllarGCt..-i.tk:e I---lData_
50<_Ill'DlecIIGr9.G<._for Speol........
lAofet aft<!R-"'ri,.Llf.~lIpaQi1ied
_Group
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I Sif.Speci1i c ~Hablfat A....lal>l'''1 00l<II
Quality IAdleu forHAIllTATIIIIOllELIndividualStudySft.
T _
I "Ia~:~~ry I ,.,:r~.
Crlterio
(Repre $emotiYe
GrOllP).
(Habitat Twel
(Micr'ohobitat Stuctt Sit.l
.J.tte.U.I
MAINSTEM DtSCHAR
SEASON
(River Se
IFR MODEL
!!1eJLI.r-
SPECIES I
LIFE HISTORY PH¥E
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Figure II-2.Schematic diagram showing the integration of physical
processes and the habitat response components of the
Relationships Model.
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III.FISH RESOURCES AND HABITAT TYPES
Overview of Susitna River Fish Resources
F'ish resources in the Susitna River comprise a major portion of the
Cook Inlet commercial salmon harvest and provide fishing opportunities
for sport angl ers.Anadromous speci es that form the base of commer-
cial and sport fisheries include five species of Pacific salmon;
chinook,coho,chum,sockeye,and pink.Resident species found in the
Susitna River basin include Arctic grayling,rainbow trout,lake
.trout,burbot,Dolly Varden,and round whitefish.Fish species that
inhabit the Susitna River are listed in Table III-I.
Adult Salmon Contribution to Commercial Fishe~'y
With the exception of sockeye and chinook salmon,the majority of the
commercial salmon catch in upper Cook Inlet originates in the Susitna
River basin (Barrett et al.1984).The long-tenn average annual catch
of 3.1 million fish is worth approximately $17.9 million to the
commercial fishing industry (K.Florey,ADF&G,pers.comm.1984).In
recent years commercial fishermen in upper Cook Inlet have landed
record numbers of salmon with over 6.2 mill ion salmon caught in 1982
and over 6.7 million fish in 1983 (Table 111-2).
The most important species to the upper Cook Inlet commercial fishing
industry is sockeye salmon.In 1984,the sockeye harvest of 2.1
million fish in was valued at $13.5 million (K.Florey,ADF&G pers.
comm.1984).The estimated contribution of Susitna River sockeye to
the industry is 10 to 30 percent (Barrett et al.1984),which,in 1984
was between 210,000 and 630 ,000 fi sh.Thi s represented a va 1ue of
between $1.4 million and $4.1 million.
Chum and coho salmon are the second and third most valuable commercial
species.In 1984,the chum salmon harvest of 684,000 fish was valued
I II-I
Table III-I.Common and scientific names of fish species recorded
from the Susitna River Basin (from Alaska Dept.of Fish
and Game,Susitna Hydro Aquatic Studies)
.....
Scientific Name Common Name
'Petromyzontidae
Lampetra japonica
Salmonidae
Coregonus laurettae
Coregonus pidschian
Oncorhynchus gorbuscha
Oncorhynchus keta
Oncorhynchus kisutch
Oncorhynchus nerka
Oncorhynchus tshawytscha
Prosopium cylindraceum
Sa 1mo ga i rdneri
Salvelinus malma
Salvelinus namaycush
Thymallus arcticus
Osmeridae
Thaleichthys pacificu~
Esocidae
Esox lucius
Catostomidae
Catostomus catostomus
Gadidae
Lota lota
Gasterosteidae
Gasterosteus aculeatus
Pungitius pungitius
Cottidae
Cottus spp.
II 1-2
Arctic lamprey
Bering cisco
humpback whitefish
pink salmon
chum salmon
coho salmon
sockeye salmon
chinook salmon
round whitefi sh
rainbow trout
Dolly Varden
1ake trout
Arctic grayl ing
eulachon
northern pike
longnose sucker
burbot
threespine stickleback
ninespine stickleback
sculpin
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Table 111-2.Commercial catch of upper Cook Inlet salmon in numbers of fish by
species,1954 -1984 (from Alaska Dept.of Fish and Game,Commercial
Fisheries Div.,Anchorage,AK).
Year Chinook Sockeye Coho Pink Chum Total
1954 63,780 1,207,046 321,525 2,189,307 510,068 4,291,726
1955 45,926 1,027,528 170,777 101,680 248,343 1,594,254
1956 64,977 1,258,789 198,189 1,595,375 782,051 3,899,381
195"7 42,158 643,712 125,434 21,228 1,001,470 1,834,022
1958 22,727 477 ,392 239,765 1,648,548 471 ,697 2,860,129
1959 32,651 612,676 106,312 12,527 300,319 1,064,485 L.
1960 27,512 923,314 311 ,461 1,411,605 659,997 3,333,889
1961 19,210 1,162,303 117,778 34,017 349,628 1,683,463
1962 20,210 1,147,573 350,324 2,711 ,689 970,582 5,200,378
r 1963 17,536 942,980 197,140 30,436 387,027 1,575,119
1964 4,531 970,055 452,654 3,231,961 1,079,084 5,738,285
"1965 9,741 1,412,350 153,619 23,963 316,444 1,916,117
1966 9,541 1,851,990 289,690 2,006,580 531,825 4,689,626
1967 7,859 1,380,062 177,729 32,229 .296,037 1,894,716
1968 4,536 1,104,904 470,450 2,278,197 1,119,114 4,977,201
1969 12,398 692,254 100,952 33,422 269,855 1,108,881
1970 8,348 731,214 275,296 813,895 775,167 2,603,920
1971 19,765 636,303 100,636 35,624 327,029 1,119,357
1972 16,086 879,824 80,933 628,580 630,148 2,235,571
~1973 5,194 670,025 104,420 326,184 667,573 1,773,396
1974 6,596 497,185 200,125 483,730 396,840 1,584,476
1975 4,780 684,818 227,372 336,359 951,796 2,205,135,-1976 10,867 1,664,150 208,710 1,256,744 469,807 3,610,278
1977 14,792 2,054,020 192,975 544,184 1,233,733 1,049,704
1978 17,303 2,622,487 219,234 1,687,092 571,925 5,118,041
1979 13,738 924,415 265,166 72,982 650,357 1,926,658
1980 12,497 1,584,392 283,623 1,871,058 387,078 4,138,648
1981 11 ,548 1,443,294 494,073 127,857 842,849 2,919,621
1982 20,636 3,237,376 777 ,132 788,972 1,428,621 6,252,737
1983 20,396 5,003,070 520,831 73,555 1,124,421 6,742,273 \-\
1984 8,800 2,103,000 443,000 623,000 684,000 3,861,800
,....,Average 19,247 1,340,339 263,785 1,576,646 659,190 3,058,170I
(even)
120,416-(odd)
,....
II 1-3
at $2.0 million,while the coho salmon harvest of 443,000 fish was
worth $1.8 million (K.Florey,ADF&G,pers.comm.1984).The
estimated contribution of Susitna River chum to the upper Cook Inlet
fi shi ng industry is estimated at 85 percent,whi 1e coho is
approximately 50 percent (Barrett et al.1984).
Pink salmon is the least desirable of the commercial species in upper
Cook Inlet,with a salmon harvest of 623,000 fish worth an estimated
$0.5 million (K.Florey,ADF&G,pers.comm.1984).Susitna River pink
.salmon contributed about 85 percent to this amount (Barrett et al.
1984).
Since 1964,opening of the commercial salmon season in upper Cook
Inlet has been delayed until late June,by which time most chinook
salmon have entered their natal streams and harvest of them is
incidental to the commercial catch.In 1984,the 8,800 chinook
harvested in upper Cook Inlet had a commercial value of $0.3 million
(K.Florey,ADF&G,pers.comm.1984).The Susitna River contribution
of chinook salmon is estimated at about 10 percent of the total catch
(Barrett et al.1984).
From 1981 to 1984 sockeye,chum,and coho salmon harvests,which
account for over 95 percent of the commercial value in the fishery,
have exceeded the long-term average catches for those speci es
(refer Table 111-2).Record catches for coho and chum were recorded
in 1982 and for sockeye in 1983.
Sport Fishing
The Susitna River,along with many of its tributaries,provides a
multi-species sport fishery.Between 1978 and 1983,the Susitna River
and its tributaries have accounted for an annual average of 127,100
angl er days of sport fishi n9 (Ni 11 s 1979,1980,1981,1982,1983,
1984).This represents approximately 13 percent of the 1977-1983
annual average of 1.0 million total angler days for the Southcentral
II 1-4
-
.,...
I
I
I
r
r""
I
r
-
-
r1egion.Most of the sport fishing in the Susitna Basin occurs in the
lower Susitna River from Alexander Creek (RM 9.8)upstream to the
Pa rks Hi ghway (RM 84).
Sport fishing occurs mainly in tributaries and at tributary mouths,
while the mainstem receives less fishing activity.In the Susitna
River coho and chinook salmon are most preferred by anglers with many
pi nk salmon taken duri ng even-year runs.In fact,when compared to
the estimated total coho escapement,the annual sport harvest of coho
salmon in the Susitna River is significant.In 1983,almost one of
every five coho salman entering the Susitna River was caught by sport
anglers (Table III-3).The annual harvest of chinook salmon in the
Susitna River has increased from 2,850 fish in 1978 to 12,420 fish in
1983 (Table 111-4).During this period,the contribution of the
Susitna River chinook sport harvest to the Southcentral Alaska chinook
sport harvest has inc reased from 11 to 22 percent.Of the res i dent
species in the Susitna River,rainbow trout and Arctic grayling are
caught by anglers in the largest numbers (Mills 1984).
Subsistence Fishing
The only subsistence fishery on Susitna River fish stocks that is
officially recognized and monitored by the Alaska Department of Fish
and Game is near the village of Tyonek,approximately 30 miles (50 km)
southwest of the Susitna River mouth.The Tyonek subsistence fishery
was reopened in 1980 after being closed for 16 years.From 1980
through 1983,the annual Tyonek subsistence ha rvest averaged 2,000
chinook,250 sockeye,and 80 coho per year (Browning 1984).
I II-5
Table 111-3.Summary of commercial and sport harvest of the Susitna River basin adult salmon returns.
Commercial Harvest SpQrt Harvest
Species
Upper 1
Cook Inlet
Ha rves t
Estimated 2
Percent Susitna
Estimated
Susitna
Harvest
Estimated
.Sus itna 3
Escapement
Estimated
Total
Run
Susitna
Basin
Sport 4
Harvest
Percent of
Escapement
I-<......
I-<
I
0,
Sockeye
81
82
83
84
Phlk
81
82
83
84
Chulll
81
H2
B3
84
Coho
81
82
83
134
Chinook
81
82
133
84
1,443,000
3,237,000
5,003,000
2,103,000
128,000
789,000
74,000
623,000
843,000
1,429.000
1,124.000
684,000
494.000
777,000
521 ,000
443,000
11.500
20.600
20,400
8,800
Mean
20
20
10
20
85
85
85
85
85
85
85
85
50
50
50
50
10
10
10
10
Range
(10-30)
(10-30)
(l0-30)
(l0-30)
288.600
647.400
500.300
420,600
108,800
670.650
62.900
529.550
716,550
1,214,650
955.400
581.400
247,000
388,500
260,500
221,500
1,150
2.060
2,040
880
287,000
279,000
185,000 5605.800
127,000
1,318,000
150,000
3,629,9005
297,000
481,000
290,000 5
812,700
68,000
148,000
45.000 5
190.100
---6
,250,000
575,600
926,400
685,300
1.026,400
235,800
1.988,650
212.900
4.159,450
1.013.550
1,695,650
1,245,400
1.394,100
315.000
536,500
305,500
411,600
251,000
1,283
2,205
5,537
8,660
16.822
4,656
4,207
6,843
5,233
9,391
16,664
8,425
7,576
10,521
12,420
0.4
0.8
3.0
6.8
1.3
3.1
1.4
1.4
1.8
13.8
11.3
18.7
~AOF&G Comn~rcial Fisheries Division
3 B.Barrett,ADF&G Su Hydro,February 15,1984 Workshop Presentation
Yentna Station (RM 18,TRM 04)+Sunshine Station (RM 80)estimated escapement;+5%for sockeye
t 48%for pink,+5%for chum,+85%for coho (8.Barrett,ADF&G Su Hydro,February 15,1984
4 Workshop Presentation).
h Mills 1982,1983,1984
~I---Iathorn Station (RM 22)escapements (Barrett et al.1985)
BarTett et a 1.1985
•J I )I J J I ]1 )1 .~
-1 1 }-1 1 r------_.----,'---'-~~.r~,'-c~1
Table 111-4.Sport fish harvest for Southcentral Alaska and Susitna Basin in numbers of fish by species,1978-1983 (from Mills 1979,1980,1981,
1982,1983,1984).
Arctic Grayling Rainbow Trout Pink Salmon Coho Salmon Chinook Salmon Chum Salmon Sockeye Salmon
South-Susitna South-Susitna South-Susitna South-Susitna South-Susitna South-Susitna South-Susitna
Year central Basin central Basin central Basin central Basin central Basin centra·l Basin central Basin
1978 47,866 13,532 107,243 14,925 143,483 55,418 81,990 15,072 26,415 2,843 23,755 15,667 118,299 845
1979 70,316 13,342 129,815 18,354 63,366 12,516 93,234 12,893 34.009 6,910 8,126 4,072 77 ,655 1,586
1980 69,462 22,083 126,686 15,488 153,794 56,621 127.958 16,499 24,155 7,389 8,660 4,759 105,914 1,304
1981 63,695 21,216 149,460 13,757 64,163 8,660 95,376 9,391 35,822 7,576 7,810 4,207 76,533 1,283
>-I 1982 60,972 18.860 142,579 16,979 105,961 16,822 136,153 16,664 46,266 10,521 13,497 6,843 128,015 2,205
>-I
I---<
I 1983 56,896 20,235 141,663 16,500 47,264 4,656 87.935 8,425 57.094 12,420 11,043 5,233 170,799 5,537......,
Average 61,535 18,211 132,908 16,000 134,413 42,954 103,774 13,157 37,294 7.943 12,149 6.797 112.869 2,128
(even)(even)
58.264 8.611
(odd)(odd)
Relative Abundance of Adult Salmon
Major salmon-producing tributaries to the Susitna River include the
Yentna River drainag.e (RM 28),the Chul itna River drainage (RM 98.6),
and the Talkeetna River drainage (RM 97.1).Numerous other smaller
tributaries also contribute to the salmon production of the Susitna
River.The .average salmon escapements at four locations in the
Susitna River for 1981 through 1984 are presented in Table 111-5.
The minimum Susitna River escapements of four salmon species can be
estimated for 1981 through 1984 by adding the escapements at Yentna
Station (RM 28,TRM 04)and Sunshine Station (RM 80)(Barrett et al.
1984).These total es capements a re cons i dered mi nimums because they
do not include escapements below RM 80,except at the Yentna River
(Barrett et a1.1984).The four-year averages of minimum Susitna
River escapements for sockeye,chum and coho salmon are presented in
Table 111-5.The minimum Susitna River escapement for pink salmon is
reported in Table 111-5 as a two-year average escapement for o~d-year
runs (1981,1983)and a two-year average escapement for even-year runs
(1982,1984).This separation was made beca-use pink salmon runs are
numerically dominant in even years (Barrett et al.1984).
Escapements of chinook salmon at Yentna Station have not been quan-
tified because most of the run passes the station before monitoring
begins (ADF&G,Su Hydro 1981,1982b;Barrett et a1.1984,1985).
Therefore,a minimum Susitna River escapement for chinook salmon
cannot be estimated by the same method used for the other salmon
species.Chinook escapements have been estimated at Sunshine Station
in 1982, 1983,and 1984 (Barrett et al.1984,1985).The three-year
average of chinook escapements at Sunshine Station is presented in
Table 1II-5.
Most salmon spawn in the Susitna River and its tributaries below
Talkeetna Station (RM 103)(ADF&G,Su Hydro 1981,1982b;Barrett et
al.1984,1985).Important chinook spawning areas are Alexander Creek
(RM 9.8),Lake Creek in the Yentna River drainage (RM 28),the Deshka
II 1-8
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-1 )1 1 },.~.~1 "..-.),.J ~~-'i -~,~~J "C~C)~.~1 ==~1
Table 111-5.Average salmon escapements in the Susitna River by species and location (from Barrett et a1.1984,
1985)•
Location
Sockeye l Chum 2 Coh0 2 Pink 3River~lil e
Yentoa Station 126,750 21,200 19,600 Odd 48,400
RM 28,TRM 04 Even 408,300
Sunshine Station 121,650 431,000 43,900 Odd 45,000
RM 80 Even 730,100
Talkeetna Station 6,300 54,600 5,700 Odd 5,900
RM 103 Even 125,500
Curry Stati on 2,400 28,200 1,600 Odd 3,300
RM 120 Even 87,900
Minimum Susitna 5 248,400 452,200 63,500 Odd 93,400
t--t River Even 1,138,400o--t
t--t
I
'-D
Chinook 4
88,200
16,700
13 ,000
Location Total
Odd 215,950
Even 575,850
Odd 729,750
Even 1,414,840
Odd 89,200
Even 208,800
Odd 48,500
Even 133,100
Odd 857,500
Even 1,902,500
1 Second-run sockeye escapements.Four-year average of 1981, 1982,1983,and 1984 escapements.
2 Four-year average of 1981, 1982, 1983,and 1984 escapements.
3 Odd is average of 1981 and 1983 escapements.Even is average of 1982 and 1984 escapements.
4 Three-year average of 1982,1983,and 1984 escapements.Dashes indicate no estimate.
5 Summation of Yentna Station and Sunshine Station average escapements.Does not include escapement to the
Susitna River and tributaries below RM 80,except the Yentna River (RM 28).
River (RM 40.5),and Prairie Creek in the Talkeetna River drainage (RM
97.1)(Barrett et ale 1984,1985).Most sockeye salmon spawn in the
Yentna,Chul itna (RM 98.6)and Tal keetna drainages (Barrett et al.
1984,1985).The Yentna River is also an important pink salmon
spawning area (Barrett et al.1984).The primary area of chum salmon
spawning is the Talkeetna River tBarrett et al.1984,1985).Coho
salmon spawn mainly in tributaries below RM 80 (Barrett et ale 1985).
In the middle reach of the Susitna River,chum and chinook are the
most abundant salmon,excluding even-year pink salmon (Barrett et ale
1984,1985).In this river reach,salmon escapements have been
monitored at Talkeetna (RM 103)and Curry (RM 120)Stations since 1981
(ADF&G,Su Hydro 1981,1982b;Barrett et al.1984,1985).
The contribution of the middle Susitna River salmon escapements to the
Susitna River salmon runs can be estimated for 1981 through 1984 by
dividing the Talkeetna Station escapements into the minimum Susitna
Ri ver escapements.Based on the average escapements presented in
Table 111-5,the average percent contribution in 1981 through 1984 for
the middle Susitna River is:2.5 percent for sockeye,12.1 percent
for chum,9.0 percent for coho,6.3 percent for odd-year pink,and
11.0 percent for even-year pink salmon.These estimates should be
considered maximum values because (1)the minimum Susitna River
escapements,as previously discussed,do not include escapements below
RM 80 (except the Yentna River);and (2)the Talkeetna Station escape-
ments overestimate the number of spawning salmon in the middle reach.
This overestimation is apparently due to milling fish that return
downstream of Talkeetna Station to spawn.
The number of fish that reach Talkeetna Station and later move
downstream to spawn is significant.In 1984,83 percent of the
sockeye,75 percent of the chum,75 percent of the coho,85 percent of
the pink,and 45 percent of the chinook salmon escapements at
Talkeetna Station were milling fish that returned downstream of
Talkeetna Station to spawn (Barrett et al.1985).If the escapement
to Talkeetna Station is reduced to account for the milling factor,the
I II-I0
-
-
-
-
-
1T"il
contribution of middle Susitna River escapement to the minimum basin
escapement in 1984 becomes:0.8 percent for sockeye,3.1 percent for
chum,2.6 percent for coho,and 1.9 percent for pink salmon.Chinook
salmon were not included in this analysis because of the lack of
minimum Susitna River escapements,as previously discussed.
~
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r
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1
l
r
r
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-
-
II 1-11
____,•4 .......__.--------.----------_
Distribution and Timing of Juvenile Salmon and Resident Species
Juvenil e Salmon
Most chum salmon rear in the middle Susitna River from May through
mid-August,while juvenile pink salmon spend little time in this reach
(Dugan et al.1984).The outmigration of juvenile chum at Talkeetna
Station (RM 103)extends from May through mid-August,whereas most
juvenile pink salmon leave this reach of river by June (Roth et al.
1984).Outmigration timing of pink and chum juveniles is positively
correlated with mainstem discharges (Roth et al.1984).
Juvenile chinook and sockeye salmon rear from one to two years in the
Susitna River,while coho salmon rear from one to three years before
outmigrating (Roth et al.1984).Although some age 0+juveniles of
chinook,coho,and sockeye salmon move out of the middle Susitna River
throughout the summer,peak downstream movements at Talkeetna Station
occur in June,July,and August (Roth et al.1984).Chinook,coho,
and sockeye juveniles that remain in the middle Susitna River utilize
summer rearing habitats until September and October,when they move to
overwintering habitats.Chinook juveniles rear primarily in
tributaries and side channels.In 1983,side channel use was highest
in July and August (Dugan et al.1984).Most coho juveniles use
tributaries and upland sloughs for summer rearing (Dugan et al.1984).
Sockeye salmon rear principally in natal side and upland sloughs
(Dugan et al.1984).Age 1+chinook,coho,and sockeye,and age 2+
coho outmigrate primarily in June at Talkeetna Station (Dugan et al.
1984).
Resident Species
Rainbow trout and Arctic grayling spawn and rear principally in
tributary and tributary mouth habitat of the middle Susitna River.A
limited amount of rearing occurs in mainstem-influenced habitats,and
both species use the mainstem for overwintering.Burbot are found
almost exclusively in mainstem,side channels,and backwater areas of
II I -12
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r
I
r-
I
-
-
side sloughs (Sundet and Wenger 1984).Estimates of relative
abundance in 1984 indicated that round whitefish are the most abundant
resident fish species in the middle river,having highest densities in
side sloughs and tributaries (Sundet and Pechek 1985).They may,
however,overwinter in the mainstem.Humpback whitefish are
relatively scarce in the middle river (Sundet and Pechek 1985).
Longnose sucker,Dolly Varden,lake trout,and threespine stickleback
are other species found in this segment of the river.
1II-13
Identification and Utilization of Habitat Types
The variety of primary,secondary and overflow channels that exist
withi n the Tal keetna-to-Devi 1 Canyon segment of the Sus itna Ri ver
provides a great diversity in aquatic habitat conditions.Six major
aquatic habitat types,based on similar morphologic,hydrologic,and
hydraulic characteristics,have been identified within this river
segment:mainstem,side channel,side slough,upland slough,
tributary,and,tributary mouth (Fig.III-I).Within these aquatic
habitat types,fish habitat of varying quantities and quality may
exist depending upon site-specific thermal,water quality,channel
structure,and hydraulic conditions.Differentiation of aquatic
habitat types is useful for evaluating seasonal movement and utili-
zation patterns if fusg and for identifying microhabitat preferences
of the fish species/life stages which inhabit the middle Susitna
River.
Mainstem Habitat
Mainstem habitat is defined as those portions of the Susitna River
which normally convey the largest amount of streamflow throughout the
year.Included in this aquatic habitat category are both single and
multiple channel reaches,as well as poorly defined water courses
flowing through partially vegetated gravel bars or islands.
Mainstem habitats are thought to be used predominantly as migrational
corridors by adult and juvenile salmon during summer.However,
isolated observations of chum salmon spawning at upwelling sites along
shoreline margins have been reported (ADF&G,Su Hydro 1982b).
Mainstem habitats are also used by several resident species,most
notably Arctic grayling,burbot,longnose sucker,rainbow trout,and
whitefish (Sundet and Wenger 1984).
II 1-14
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-
r
1""'"
I
-
-
-
Note:A _ore de'atted de.crlptlon of th•••hab'tat type.
can be found 'n th ••••ctlon 01 th ••report.
..........,':'.::.
"'"...~:.
LEGEND
L Mainstem Habitat
2.Side Channel Habitat
3.Side Slough Habitat
4.Upland Slough Habitat
5.Tribut<lry Habitat
6.Tributary Moulh Habitat
Figure III-I.General habitat types of the Susitna River
(ADF&G,Su Hydro I983a)
III-IS
Turbid,high-velocity,sediment-laden summer streamflows and low,
cold,ice-covered,clearwater winter flows are characteristic of
mainstem habitat type.Channels are relatively stable,high gradient
and normally well-armored with cobbles and boulders.Interstitial
spaces between these large streambed particles are generally filled
with a grout-like mixture of small gravels and glacial sands with
isolated deposits of small cobbles and gravels.However,the latter
are usually unstable.
Groundwater upwell i ngs and cl earwater tributary i nfl ow appear to be
inconsequential determinants of the overall characteristics of main-
stem habitat except during winter when they dominate water quality
conditions of the mainstem.
Side Channel Habitats
Side channel habitats are sections of the river which normally convey
streamflow during the open water season,but become appreciably
dewatered during periods of low flow.For convenience of classifi-
cation and analysis,side channels are defined as conveying less than
10 percent of the total flow passing a given location in the river.
Side channel habitat may exist in well-defined channels,or in poorly-
defined water courses flowing through partially submerged gravel
islands located in mid-channel or along shoreline margins of mainstem
habitat.
Rearing juvenile chinook appear to use side channel habitats most
extensively,particularly during July and August (Dugan et al.1984).
A limited amount of chum salmon spawning also occurs in side channel
habitats where upwelling and suitable velocities and substrate are
present (Estes and Vi ncent-Lang 1984d).Resi dent speci es,such as
grayling,rainbow trout,burbot,and whitefish,also use these
habitats.
I II-16
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.....
-
-
-
In general,the turbidity,suspended sediment,and thermal character-
istics of side channel habitats reflect mainstem conditions,except in
qui escent areas,where suspended sediment concentrati ons are 1ess.
Side channel habitats are characterized by shallower depths,lower
velocities,and smaller streambed materials than mainstem habitats.
However,side channel velocities and substrate composition often
provide suboptimal habitat conditions for both adult and juvenile
fish.
The presence or absence of clearwater inflow,such as groundwater
upwellings or tributaries,is not considered a critical component in
the designation of side channel habitat.However,a strong positive
correlation exists between the location of such clearwater inflows and
the location of chum salmon spawning sites in these habitats (Estes
and Vincent-Lang I984d).In addition,tributary and groundwater
inflow prevents some side channel habitat from becoming completely
dlewatered when mainstem flows recede in September and October.These
clearwater areas are suspected of being important for primary
production prior to the formation of a winter ice cover.
Side Slough Habitats
~Iith the exception of the clearwater tributaries,side slough habitats
alre probably the most productive of all the middle Susitna River
clquati c habitat types.Si de slough habitats typi ca lly exi st in
overflow channels or old side channels which only convey mainstem flow
cluring periods of high streamflow or breakup.Clearwater inflows from
local runoff and/or ~pwelling maintains streamflow through side slough
habitats when they are not overtopped by high mainstem discharge.
t\non-vegetated all uvi a1 berm connects the head of the slough to the
mainstemor a side channel with a well-vegetated gravel bar or island
paralleling the slough and separating it from the mainstem (or side
channel).During intermediate and low-flow periods,mainstem \',ater
surface elevations are insufficient to overtop the alluvial berm at
III-17
---,-------------.......-------------------------
the upstream end (head)of the slough.However,the mainstem stage at
these flows is often sufficient at the downstream end (mouth)of the
slough to cause a backwater effect to extend a few hundred feet
upstream into the slough (Trihey 1982).
In the middle Susitna River approximately 80 percent of all
non-tributary spawning by chum salmon and essentially all sockeye
salmon spawning occurs in unbreached side slough habitat (ADF&G,Su
Hydro 1981,1982b;Barrett et al.1984).In early spring,large
numbers of juvenile chum and sockeye salmon can be found in unbreached
side sloughs.During summer,moderate numbers of juvenile coho and
chinook make use of side-slough habitats,with chinook densities
increasing during the fall-winter transition (Dugan et al.1984).
Small numbers of resident species,such as rainbow trout,Arctic
grayling,burbot,round whitefish,cottids,and longnose suckers,are
also found in side slough habitats.
Considerable variation in water chemistry has been documented among
side sloughs.This is principally a function of local runoff pat-
terns,basin characteristics,and groundwater upwelling when the side
sloughs are not overtopped.Once overtopped,side sloughs display the
water quality characteristics of the mainstem (ADF&G,Su Hydro 1982a).
During periods of high mainstem discharge,the water surface elevation
of the mainstem is often sufficient to overtop the alluvial berms at
the heads of some sloughs.When thi s occurs,di scharge through the
side slough increases markedly.Generally from less than 5 cfs to
100 cfs or greater.Such overtopping events affect the thermal,water
quality,and hydraulic conditions of side slough habitat (ADF&G,Su
Hydro 1982a).Depending upon its severity and frequency,overtopping
may flush organic material and fine sediments from the side slough or
totally rework the channel geometry and substrate composition.
Streambed materials in side slough habitats tend to be a heterogeneous
mixture of coarse sands,gravels and cobbles,often overlain by fine
I II-18
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-
,...
1
1
r-
I,
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"""
glacial sands in quiescent areas.Perhaps because of the upwelling or
the less frequent conveyance of mainstem water,streambed materials in
side slough habitats do not appear to be as cemented or grouted as
similar sized particles would be in side channel habitats.
When not overtopped,surface water temperatures in side sloughs
respond independently of mainstem temperatures (ADF&G,Su Hydro
1982a).Surface water temperatures in unbreached side sloughs are
i nfl uenced by the temperature of groundwater upwell i ng,the tempera-
ture of surface runoff,and climatologic conditions.In many
instances the thermal effect of the upwelling water is sufficient to
maintain relatively ice-free conditions in these areas throughout
winter (Trihey 1982;ADF&G,Su Hydro 1983c).
Upland Slough Habitats
Upland slough habitats are clearwater systems which exist in relic
side channels or overflow channels.They differ in character from
side sl~ugh habitats in that the elevation of the upstream berm is
sufficient to prevent overtopping in all but the most extreme flood or
ice jam events.Consequently,upland sloughs typically possess steep,
well-vegetated streambanks,near-zero flow velocities,and sand or
silt covering larger substrates.In addition,active or abandoned
beaver dams and food caches are commonly observed in these habitats.
The primary influence of mainstem or side channel flow on an adjacent
upland slough is the regulation of water depth in the slough by
backwater effects.The water surface elevation of the adjacent
mainstem or side channel often controls the water surface elevation at
the mouth of the upland slough.Depending upon the rate at which the
mainstem water surface elevation responds to storm events relative to
the response of local runoff into the upland slough,turbid mainstem
water may enter the slough.The rapid increase in mainstem water
surfacee1eva ti ons and suspended sediment concentrations associated
with peak flow events is suspected of being a primary transport
III-19
~---------_._------------.......---------------------
mechanism of fine sediments into the backwater areas of upland
sloughs while local surface water inflow and bank erosion may be major
contributors of sediments in reaches upstream of backwater areas and
beaver dams.
Although upwelling is often present in upland sloughs,little spawning
occurs in these habitats (Barrett et al.1984).The most extensive
use is by rearing juvenile sockeye and coho salmon (Dugan et al.
1984).Resident species common in upland sloughs include round
whitefish and rainbow trout.
Tributary Habitats
Tributary habitats reflect the integration of their watershed charac-
teristics and are independent of mainstem flow,temperature,and
sediment reg"imes.Middle Susitna River tributary streams convey clear
water which originates from snowmelt,rainfall runoff,or groundwater
base flow throughout the year.
Tributaries provide the only reported spawning areas for chinook
salmon and nearly all of the coho and pink salmon spawning areas in
the middle Susitna River (Barrett et al.1984).Also,approximately
one-third of the chum salmon escapement to the middle Susitna River
spawn in tributary habitats.Pink salmon juveniles outmigrate shortly
after emergence and most juvenile chum leave within one to three
months.However,a large percentage of emergent chinook and coho
remain in tributary streams for several months following emergence
(Dugan et al.1984).Resident species,particularly Arctic grayling
and rainbow trout,depend principally on tributary streams for
spawning and rearing.
Tributary Mouth Habitat
Tributary mouth habitat refers to that portion of the tributary which
adjoins the Susitna River.The areal extent of this habitat responds
I II-20
""""
-
-
-
r
'Il
-i
-
-
-
-
-
to changes in mainstem discharge.By definition,this habitat extends
from the uppermost point in the tributary influenced by mainstem
backwater effects to the downstream extent of its clearwater plume.
Though velocities could be limiting,tributary mouth habitat
associated with the larger tributaries within the middle Susitna River
also provides significant spawning habitat for pink and chum salmon
(JBarrett et al.1984).This habitat type is an important feeding
station for juvenile chinook (ADF&G,Su Hydro 1983e),rainbow trout,
and Arctic grayling (Sundet and Wenger 1984),especially during
periods of salmon spawning activity.
II 1-21
-----,-------------------------------------
Selection of Evaluation Species
Selection of evaluation species for use in the IFRS is consistent with
the guidelines and policies of the Alaska Power Authority,Alaska
Department of Fish and Game,and U.S.Fish and Wildlife Service (USFWS
1981;ADF&G 1982;APA 1982).These guidelines imply that species with
commercial,subsistence,and recreational uses are given high
priority.The species of greatest concern are those utilizing
habitats that will be most altered by the project.The following
discussion provides a synopsis of the baseline data used in the
selection of primary and secondary evaluation species.
Side slough and side channel habitats are expected to be affected most
si gnifi cantly by project operati on.Consequently,the speci es and
life stages considered for evaluation were those which use these two
habitats most extensively.Chum salmon spawners and incubating
embryos,and juvenile chinook salmon were selected,for the reasons
discussed below,as primary evaluation species and life stages.
Secondary evaluation species and life stages that may be considered in
subsequent analyses of flow effects on aquatic habitats include:chum
salmon juveniles and returning adults,chinook salmon returning
adults,all freshwater life phases of sockeye and pink salmon,rearing
and overwintering rainbow trout,coho salmon juveniles and returning
adults,rearing and overwintering Arctic grayling,and all life phases
of burbot.
Salmon spawning surveys conducted during 1981-83 by the Alaska
Department of Fish and Game (Barrett et al.1984)indicate that tribu-
taries and side sloughs are the primary spawning areas for the five
species of Pacific salmon that occur in the middle reach of the
Susitna River (Figure II1-2).Comparatively small numbers of salmon
spawn in mainstem,side channel,upland slough,and tributary mouth
habitats.Chum and sockeye are the most abundant salmon species that
spawn in non-tributary habitats in the Talkeetna-to-Devil Canyon reach
of the Susitna River (Barrett et al.1984).The estimated number of
II 1-22
-
-
MS SC SL T
LEGEND
MS -MAl NSTEM
SC -SIDE CHANNEL
SL -UPLAND and SIDE SLOUGHS
T -TRIBUTARIES
~-PRIMARY SPAWNINe HABITAT
•-SECONDARY SAlWNINe HABITAT
MS SC SL T
COHO
MS SC SL T
CHINOOK
SOCKEYE
MS SC SL T
PINK
lIS SC SL T
CHUM
-
-
Figure III-2.Relative distribution of salmon spawning within
different habitat types of the middle Susitna
River (Estes and Vincent-Lan0 1984c).
II I -23
chum salmon spawning in non-tributary habitats within the middle
Susitna River averaged 4,200 fish per year for the 1981-83 period of
record (Barrett et al.1984).This represents about two-thirds of the
peak survey counts ina 11 habitats duri ng 1981-1983 (Ba rrett et a 1.
1984).Approximately 1,600 sockeye per year (99 percent of peak
survey counts)spawned in slough habitat during the same period.
Limited numbers of pink salmon utilize side channels and side sloughs
for spawning during even-numbered years (Barrett et al.1984).
Similarly,only a few coho salmon spawn in non-tributary habitats of
the Susitna River (Barrett et al.1984).
Approximately 10,000 chum salmon have returned annually to the middle
Susitna River to spawn during the 1981-1983 period of record,of which
nearly half spawned in tributaries.Approximately 80 percent of those
non-tributary spawners spawned in side slough habitats.Sloughs 21,
11,9,9A and 8A generally account for the majority of slough spawning
(ADF&G,Su Hydro 1981,1982b;Barrett et al.1984).Extensive surveys
of side channel and mainstem areas have documented comparatively low
numbers of spawners and spawning areas in side channel and mainstem
habitats (ADF&G,Su Hydro 1981,1982b;Barrett~t al.1984).
Withi n the Tal keetna-to-Devi 1 Canyon reach,spawning sockeye salmon
are distributed among eleven sloughs.Sloughs 11,8A,and 21
accounted for more than 95 percent of the sockeye spawni ng in the
middle Susitna River during 1981-1983 (Barrett et al.1984).In 1983,
11 sockeye salmon were observed spawning alongside 56 chum salmon in
the mainstem approximately 0.5 miles upstream of the mouth of the
Indian River (Barrett et al.1984).This is the only recorded
occurrence of sockeye salman spawning in middle Susitna River areas
other than slough habitats.
Chum salmon spawn at all of the locations where sockeye spawning has
been observed (Barrett et al.1984).This overlap is likely a result
of similar timing and habitat requirements (Barrett et al.1984;Estes
and Vincent-Lang 1984d).Chum salmon are more numerous in slough
I II -24
~.
-
-
'"""
-
""'"
-
~
,1
:1
r
I
-
.-
-
-
habitats and appear to be more constrained by passage restrictions and
low-water depth during spawning than sockeye salmon (Estes and Vincent-
Lang 1984c).Hence,the primary evaluation of habitat relationships
for analysis of project effects on existing salmon spawning in the
middle Susitna River will focus on chum salmon.
Depending upon the season of the year,juvenile salmon utilize all
aquatic habitat types found within the middle Susitna River in varying
degrees.Among the non-tributary habitats,juvenile salmon densities
are highest in sloughs and side channel areas (Fig.1II-3).Extensive
sampling for juveniles has not been conducted in mainstem habitats,
largely due to the inefficiency of sampling gear in typically deep,
fast,turbid waters.However,utilization of mainstem habitat is
.expected to be low except for low velocity shoreline margins .
Coho salmon juveniles are most abundant in tributary and upland slough
habitats which generally do not respond significantly to variations in
mainstem discharge (Klinger and Trihey 1984).Although relatively few
in number,sockeye juveniles make extensive use of upland slough and
side slough habitats within the middle Susitna River.
Juvenile chum and chinook salmon are quite abundant in the middle
Sus itna Ri ver;the most extensi ve ly used of the non-tri butary
.habitats are side sloughs and side channels (Dugan et al.1984).
These habitats respond markedly to variations in mainstem discharge
(Klinger and Trihey 1984).For this reason,chinook and chum have
been selected to evaluate project effects on juvenile salmon rearing
conditions within the middle Susitna River.Because juvenile chinook
have a longer freshwater residence period,they are a primary
eva 1uati on speci es/l ife stage whil e juvenil e chum are a secondary
evaluation species/life stage.
With the exception of burbot,important resident species in the middle
Susitna River are mainly associated with tributary habitats.Rainbow
trout and Arctic grayling,important to the basin's sport fishery,
I II -25
COHO
UPLAND SIDE SIDE
SLOUGHS CHANNELS SLOUGHS
to
I-Z
UJo 30
a:
~
TRIBUTARIES'UPLAND SIDE SIDE
SLOUGHS CHANNELS SLOUGHS
CHUM
10
o J......::/iii·:'.'.:::iii IZI2
40
50
60
t-
Z
~30
0:
UJ
D..20
o I .8 I
TRIBUTARIES UPLAND SIDE SIDE
SLOUGHS CHANNELS SLOUGHS
TRIBUTARIES UPLAND SIDE SIDE
SLOUGHS CHANNELS SLOUGHS
o~········/':~i?;~
1-4 MG;J ~~60
1-4
50 .•.·•••..•i//
......RELATIVEI
1''0 ABUNDANCE 5
m 0".';'.'::::':;'::;""OF JUVENILE
SALMON 40
~1 I-
Z Z
W 30 ~30~~n 0:
UJ
D..20
CHINOOK SOCKEYE
Figure 111-3.Relative abundance and distribution of juvenile salmon within different habitat
types of the middle Susitna River (adapted from Dugan et al.1984).
I j j J J )J ..J .1 J ].1
J"""
t
-
-
"....
-
-
spawn and rear in tributary and tributary mouth habitats.A limited
number of rainbow trout and Arctic grayling rear in mainstem-
influenced habitats (Sundet and Wenger 1984),and both species use
mainstem habitats for overwintering.Due to their use of
mainstem-influenced areas,overwintering and rearing Arctic grayling
and rainbow trout are selected as secondary evaluation species.
Btecause burbot apparently prefer turbi d habitats,they are found
almost exclusively in mainstem,side channels,and slough mouths
(Sundet and Wenger 1984).As the 1FR analysis continues,burbot and
other secondary evaluation species whose populations may be influenced
by the project will be considered for more detailed evaluation.Chum,
chinook,and pink salmon spawning and incubation in side channel and
mainstem habitats are some species and life stages that may be
evaluated.
II 1-27
....
-
-I
-
IV.WATERSHED CHARACTERISTICS AND PHYSICAL PROCESSES
INFLUENCING MIDDLE SUSITNA RIVER HABITATS
This chapter discusses numerous interrelationships among physical
processes associated with streamflow,sediment transport,water
quality and stream temperature in the middle Susitna River and also
describes their influence on the availability and quality of aquatic
habitat.These physical processes and relationships are discussed in
association with such important watershed characteristics as
climatology,topography and geology.Because of the relatively
undistrubed nature of the Susitna Basin and the limited probability of
significant disturbance occurring in the near future,land use is
considered a constant and is not discussed in this section.
Watershed Characteristics
Basin Overview
Tributaries in the upper portions of the Susitna River basin originate
from glacial sources in the Alaska Range which is dominated by Mount
Deborah (12,339 feet)and Mount Hayes (13,823 feet).Other peaks in
the Alaska Range average between 7,000 and 9,000 feet in altitude.
Tributaries in the eastern portion of the Susitna Basin originate in
the Copper River lowlands and in the Talkeetna Mountains,having ele-
vations averaging between 6,000 and 7,000 feet.Between the Alaska
Range and the Talkeetna Mounta ins are the Sus itna 1owl ands;a broad
basin increasing in elevation from sea level to 500 feet,with local
relief of 50 to 250 feet (Fig.IV-I).
In the mountainous areas above 3,000 feet elevation,discontinuous
permafrost is often present.Below 3,000 feet elevation,isolated
occurrences of permafrost can be found in association with
fine-grained soils.The Susitna basin geology consists of extensive
unconsolidated glacial deposits.Glacial moraines and outwash are
IV-I
>-<
<:
I
r'J
Figure IV-I.
+10 Rivermile lncrement:s
Scale'I":16milel
Stream network within the Susitna River Basin.
),)J c···]I J .1 J J J J J
I'*""
I
flound in many U-shaped valleys in the upland areas.Gravelly till and
outwash in the lowlands and on upland slopes are overlain by shallow
to moderately deep silty soils.The steep upper slopes have shallow
gravel and loam deposits with many bedrock exposures.On the south
flank of the Alaska Range and southern slopes of the Talkeetna
Mountains,soils are well-drained,dark,and gravelly to loamy.
Poorly drained,stony loams with permafrost are present on northern
facing slopes.Water erosion ranges from moderate to severe.
Vegetation above the tree line in the steep,rocky soils is
predominantly alpine tundra,whereas,well-drained upland soils
support white spruce and grasses.Poorly drained valley bottom soils
support muskeg while well-drained soils support mixed stands of birch
and spruce.
-The upper Susitna basin is in the continental climatic zone,while the
lower portion of the basin is in the transitional climatic zone.
Temperatures are more moderate and precipitation is less in the lower
basin than in the upper basin (Fig.IV-2).
I~
Lo...S....Hno SQ.*"
lSherman-T~_••1l'1<1 Srotl·OM)
U"",_r S'We-J1'fMI 8oah"
iSu,sHn<I GlOd«·~'(lM
STafton I
..---....,...-.....
I --'"'I ,
I \
I \
I \J \
I .,
I
I
I
I
I
I,
I,
-10
10
o
!..5
Ula:
::l...<a:w
~0
Ul...
a:<
Ul -5
C)<a::...
~
r
J FMAMJJASONO
1983/1984
Fi gu re IV -2.Average monthly air temperatures (OC)in the upper and
lower basins of the Susitna River (adapted from R&I\1
1984a,1985a;U.S.Dept.of Commerce 1983,1984).
r IV-3
Storms whi ch affect the area generally cross the Chugach Range from
the Gulf of Alaska or come from the North Pacific or southern Bering
Sea across the Alaska Range west of the upper Susitna Basin.As
expected,precipitation is much heavier in the higher elevations than
in the valleys.The heaviest precipitation generally falls on the
windward side of the Alaska Range,leaving the upper basin in somewhat
of a precipitation shadow except for the higher peaks of the Talkeetna
Mountains and the southern slopes of the Alaska Range.
Basin Hydrology
The Susitna River is typical of unregulated northern glacial rivers,
with relatively high turbid streamflow during summer and low clear-
water flow during winter.Approximately 87 percent of the total
annual flow of the middle Susitna River occurs from May through
September,and over 60 percent occurs duri ng June,July and August
(Table IV-I).Snowmelt and rainfall runoff cause a rapid rise in
streamflows during late May and early June,and over half of the
annual floods occur during this period.
Table IV-I.Summary of monthly streamflow statistics for the Susitna
River at Gold Creek from 1949 to 1982 (from Harza-Ebasco
1985g).
Monthly Flow (cfs)
Month Maximum Mean Mi nimum
January 2,452 1,542 724
February 2,028 1,320 723
March 1,900 1,177 713
Apri 1 2,650 1,436 745
May 21,890 13 ,420 3,745
June 50,580 27,520 15,500
July 34,400 24,310 16,100
August 37,870 21,905 8,879
September 21,240 13,340 5,093
October 8,212 5,907 3,124
November 4,192 2,605 1,215
December 3,264 1,844 866
Average 15,900 9,651 4,785
IV-4
-
-
IJ
.u
I
I
I
U
II
U
I
!
".i i
I I-
1 !I I-
!I
Daily streamflows are relatively high throughout the summer,
occasioned by rapid responses to highly variable precipitation
patterns.Susitna River streamflows are most variable during the
months of May and October,transition periods commonly associated with
spri ng breakup and the onset of freeze up.From November through
Apri 1,cold air temperatures cause surface runoff to freeze,and
stable but gradually declining streamflows are maintained throughout
winter by groundwater inflow and baseflow from headwater lakes .
The glaciated portions of the upper Susitna Basin have a distinct
influence on th~annual hydrograph for the Susitna River at Gold Creek
(USGS stream gage station 15292000).R&M Consultants and Harri son
(1982)state that II roug hly 38 percent of the streamflow at Gold Creek
originates above the gaging stations on the Maclaren River near Paxson
and on the Susitna River near Denal i ...It
•located on the southern
slopes of the Alaska Range,these glaciated regions receive the
greatest amount of precipitation that falls in the basin.The
glaciers,covering about 290 square miles,_or approximately 5 percent
of the basin upstream of Gold Creek~act as reservoirs storing water
in the form of snow and ice during winter and gradually releasing melt
wiater throughout the summer to maintain moderately high streamflows.
Valley walls in those portions of the upper basin not covered by
glaciers,consist of steep bedrock exposures or shallow soil systems.
Hence rapi d surface runoff ori gi nates from the gl aciers and upper
basin whenever rainstorms occur.
Susitna River streamflo~originates from glacial melt,surface runoff,
a.nd groundwater inflow.The relative importance of each of these
contributions to the total discharge of the Susitna River at Gold
Creek varies seasonally (Fig.IV-3).Although the amount of
9roundwater inflow to the middle Susitna is thought to remain fairly
constant throughout the year,its relative importance to streamflow
alnd water quality increases si gnifi cantly duri ng wi nter as the
streamflow contribution from glacial melt and surface runoff decrease.
During September as air temperatures in the upper basin fall below
IV-5
freezing,glacial melt subsides,and mainstem streamflows clear.By
November below freezing air temperatures occur throughout the basin
(refer Fig.IV-2)and streamflows have decreased to approximately one
tenth their midsummer values.Streamflow at the Gold Creek gage is
maintained by the Tyone River which drains Lake Louise,Susitna Lake
and Tyone Lake,and by groundwater inflow to several smaller
tributaries and to the Susitna River itself.
Groundwater
\
Surfa~e Runoff
I
(9.._Lakes
Ground
Water..........
WINTER
SUMMER
Figure IV-3.Estimated percent contributions to middle Susitna River
streamflow.
IV-6
-
-
-
-
....
....
-
Streamflow Variability and With-project Operations
The variabi1ity of naturally occurring annual peak flows,mean summer
discharge,and average annual streamflow for the Susitna River at Gold
Creek is illustrated in Figure IV-4.Peak flows for the Susitna River
Imrmally occur during June in association with the snowmelt flood,but
summer rainstorms often cause floods during August (Table IV-2).
Flood peaks are seldom more than double the long term average monthly
flow for the month in which they occur (R&M 1981b),however average
monthly flows for June,July,and August are nearly 2.5'times the
average annual discharge of 9700 cfs (Scully et a1.1978).Although
these streamflow statistics are not exceptionally variable,they imply
that a very large amount of water typically flows through the middle
Susitna River corridor during summer .
Table IV-2 Percent distribution of annual peak flow events for the
Susitna River at Gold Creek 1950-1982 (R&M Consultants
1981b).
Month Percent
May 9
June 55
July 9-August 24
September 3
-
-
....
The natural flow regime of the middle Susitna River is expected to be
altered by project operation.With-project streamflows will generally
be less than natural streamflows during the May through July period
(Phase I and Phase II)as water is stored in the reservoirs for
r'elease during the winter.For Phase III,streamflows will be less
than natural through the month of August (Fig.IV-5).During the May
through August period,variability of middle Susitna River streamflows
will be caused by tributary response to snowmelt and rainfall runoff
as well as from controlled releases from the reservoirs.With-project
floods would sti1l occur in late summer but would be significantly
reduced in both frequency and magnitude (Table IV-3).
IV-7
!5
100
o 80
0
0-
)(
...
1;60--
UJ
"Q::«
t-<5 40
<(I)
I Cco
20
Susltna River at Gold Creek
...',",.......,'"V I,V /\
,..;","'''"...1 ,,,.,'"\
/',,/.._...-',,,\__oJ \/""/'"'";'
I -~..."\I \I '',I \1 \__.J \ /'1 ,\
\
1 \I ,I ,I
\/'
V_.-.--'-'-'".~.................."-_.--....,•..__•--...-..0_,"--'----."./..............0'-..---""""'./'.-/""-
50 -'~
Q::
UJ25.-
!i ....
UJ eoa10z.,.
UJ
0::--0::
:::>o
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0::
2
LEGEND
Annual flood peak discharge
Average sunvner dlschar98
(June,July.August)
Average yearly discharQe
o
1950 195!5 1960 1965
WATER YEAR
1970 197!5 1980
Figure IV-4.Naturally occurring annual peak flows,mean summer discharge,and annual streamflow
of the Susitna River at Gold Creek (adapted from Harza-Ebasco 1985c as modified by
AEIDC 1985b).
,J J )J .1 .J J J I J 1
0----0
.------{I
oNoSAMJJ
MONTH
A
NATURAL
STAGE I
STAGE II
LATE STAGE
III
MFJ
•••
o
10
30
"...
-I,
!,"""Figure I'I-5.Estimated with-rroject mean monthly flows at Gold Creek
compared to natural flows (adapted from APA 1985b).
IV-9
IV-IO
-
-i
-
r-:
!
.-
!
I
-I
I
With-project streamflow during September is expected to be less
v,ariable but near to the long term average monthly natural flow for
this month.Streamflows from October through April would be greater
in magnitude and more variable than natural winter streamflows.Daily
fluctuations in streamflow are expected to occur throughout winter as
the hydroelectric project responds to meet varying electric load
demands.A family of rule curves will be used as a guide for seasonal
adjustment of flow for power generati on and downstream flow
requirements.The Alaska Power Authority proposed to limit streamflow
fluctuations resulting from appl ication of these rule curves to ±1O
percent of the average weekly discharge (Harza-Ebasco 1985b).
IV-ll
Influence of Streamflow on Habitats
Mainstem and Side Channel Habitats
Mainstem and side channel gradients within the middle Susitna River
are on the order of 8 to 14 ft/mile (Bredthauer and Drage 1982).As a
result of this steep channel gradient,mid-channel velocities are
often in the range of seven to ni ne feet per second (fps)du ri ng
normal mid-summer streamflow conditions.Mainstem velocities of 14 to
15 fps have been measured by the USGS at the Gold Creek-stream gage in
association with 62,000 to 65,000 cfs flood flows (L.Leveen,USGS,
1984,pers.comm.).For most species of fish and benthic
invertebrates high velocity streamflows are considered undesirable.
The upper limit for velocity preferred by most juvenile salmonids is
generally less than one fps and that for adults seldom exceeds 4 fps
(Estes and Vincent-Lang 1984d;Suchanek et al.1984).
Analysis of hydraulic conditions in the mainstem and large side
channels indicates that mid-channel velocities are generally
unsuitable for fish over a wide range of mainstem discharge (Williams
1985).Suitable habitat for juvenile fish is usually restricted to a
narrow zone associated with the shoreline margin.As mainstem
discharge changes,the width (surface area)of this habitat zone
remains relatively constant but moves laterally in response to water
surface elevation.Because the shoreline margins are almost void of
cover objects,habitat quality responds little to changes in the
location of the shoreline habitat zone.
Side Slough Habitats
Side sloughs are overflow channels,located along the floodplain
margins,which contain important spawning and rearing habitat for
salmon.Side slough streambed elevations are higher than those of
adjacent side channels or the mainstel11.Hence side sloughs only
convey water from the mainstem during periods of high streamflow.
When mainstem discharge is insufficient to overtop the upstream end of
IV-12
-
-
the slough,slough flow,generally less than 5 cfs,ismaintained by
tl~ibutary or groundwater inflow.Howtlver,mainstem or side channel
water surface elevations at the downstream end of the slough are
usua lly suffi ci ent to cause a backwater pool to extend a few hundred
feet upstream into the slough mouth.
Whenever the water surface elevation (stage)of the mainstem or side
channel adjacent to the slough is sufficient to overtop the head of
tl1e slough,discharge through the side slough increases markedly.
TI1ese overtoppi ng events also affect the thermal,water quality,and
hydraulic characieristics within the slough.Overtopping during
breakup and flood events generally provides adequate flow velocities
in the side slough to scour debris,beaver dams,and fine sediments
from the side sloughs.However,overtoppings associated with normal
summer stream flows (20,000 to 30,000 cfs)generally transport large
amounts of suspended sand and fine sediments into the slough which
then settle out in low velocity areas.Sedimentation is most apparent
in the backwater zone at the slough mouth where the deposition may
often exceed one foot.Overtoppi ng duri ng early June is thought to
assist the outmigration of "juvenile chum salmon.During late August
and early September,overtopping provides unrestricted passage by
adult salmon to spawning areas within the side sloughs.
The frequency at which a particular side slough (or side channel)is
overtopped varies according to the relationship betweenmainstem water
surface elevation and the elevation of the streambed at the upstream
end (head)of the slough.The mainstem discharge which provides a
water surface elevation sufficient to overtop the head of the side
slough (or side channel)is referred to as the breach i ng flow.Each
side slough and side channel has a unique breaching flow;however,
breaching flows for side channels are typically less than 20,000 cfs
whereas side slough breaching flows generally exceed 20,000 cfs.
Passage.Because of the significant influence overtopping events have
on habitat conditions and fish passage in side sloughs,special
IV-13
consideration has been given to mainstem stage-discharge relationships
and breaching flows by the study team (ADF&G,Su Hydro 1983a;Estes
and Vincent-Lang 1984a;Hilliard et al.1985).Analysis of the
thirty-five year period of streamflow record for the middle Susitna
River indicates that overtopping events occur rather frequently during
the August 12 through September 15 spawning period (Table IV-4).Side
sloughs with breaching flows of 23,000 cfs were overtopped for 19.1
percent of the evaluation period.During the thirty-five year period
of record,overtopping events were most frequently either 1-,2-or
3-days in duration (25 events);however,9 events longer than seven
consecutive days also occurred.Side sloughs or side channels with
breaching flows in the range of 16,000 to 18,000 cfs were overtopped
nearly half of the time with a large number of events (23)being
longer than seven consecutive days.
Field observations indicate adult salmon respond rapidly to improved
passage conditions and quickly enter side sloughs to spawn (Trihey
1982).Therefore frequent,but short-duration,overtopping events as
occur naturally for sloughs with brea~hing flows as high as 25,000 cfs
provide adequate passage condition.In addition,the response of the
water surface elevation of the backwater zone at the slough mouth to
increased mainstem discharge and the response of slough flow to
rainfall often provide short-term improvement of passage conditions
when the mainstem discharge is less than the breaching flow.
Insufficient data are available at this time to describe the influence
of the natural variability in slough flow on passage conditions.
Groundwater Upwelling and Intragravel Flow
Upwelling and intragravel flow have been recognized as strongly
influencing the spawning behavior of chum and sockeye salmon in Alaska
(Kogl 1965;Koski 1975;Wilson et al.1981;Estes and Vincent-Lang
1984d).Upwelling has also been credited with maintaining relatively
warm open water leads in some side channels and sloughs throughout
winter (Barrett 1975;Trihey 1982).These leads are important to the
IV-14
~,
-
-
--
I
I
-)'--,
Table IV-4.Number of ltimes during the spawning period mainstem discharge was equal to or greater than the breaching flow for the consecutive number of days and years
indicated.
AUGUST 12 THROUGH SEPTEMBER 15
Approximate
Breaching Exceedance l-day 2-day 3-day 4-day 5-day 6-day 7-day 7-day
Flow Value Total
(cts)(tl events in years events in years events in years events in years events in years events in years events in years events in years days
12000 79.6 4 4 1 1 2 2 1 1 2 2 3 3 1 1 37 34 975
16000 56.8 6 4 6 6 6 6 2 2 5 5 2 1 0 0 31 29 696
19000 38.2 5 4 5 5 7 5 7 7 4 4 3 3 4 4 23 20 468
23000 19.1 9 9 7 7 9 7 4 3 3 3 2 2 2 2 9 9 242
25000 12.7 6 6 7 6 4 4 3 3 2 2 1 1 2 2 6 6 156
27000 8.7 6 6 3 3 2 2 1 1 3 3 0 0 2 2 4 4 106
I-i 33000 4.3 1 1 1 1
1 1 1 1 1 1 1 1 1 1
2 2 48
<
I 35000 3.5 0 0 1 1 1 1 1 1 2 2 1 1 1 1 1 1 44.......
Ul 40000 2.5 2 2 2 2 1 1 1 1 0 0 2 2 1 1 0 0 32
42000 2.1 0 0 1 1 1 1 1 1 1 1 2 2 0 0 0 0
26
Based on Average Daily streamflow records for the Susitna River at Gold Creek 1950-1984.
The controlling elevation of the berm at the upstreaul end of the slough may change over time due to high flow or ice scour.
overwinter survival of incubating eggs and alevins (Vining et ale
1985)and juvenile chinook (Stratton 1985).
In river valleys where the underlying materials originate from glacial
outwash,groundwater flow patterns are often complex.In the middle
Susitna River there appears to be three main sources of subsurface
flow (upwelling)into side channel and slough habitats.
1.
2.
3.
Infiltration of surface flow from the mainstem through islands
and gravel bars which separate the sloughs and side channels from
the mainstem (intragravel flow),
Subsurface flow toward the river from upland sources (upland
groundwater component),and
Subsurface flow in the downstream direction within alluvial
materials comprlslng the flood plain of the middle Susitna River
(regional groundwater component).
"'"
-
The relative contribution of these three sources has been examined
(APA 1984b)and it appears that infiltration from the mainstem is the
primary source of subsurface flow into side channel and slough
habitats along the middle Susitna River.In addition,the response of
slough flow to changes in mainstem discharge (when the upstream berms
are not overtopped)is relatively rapid;often occurring in a matter
of hours.
The groundwater flow rate from upland sources is the least influential
of these three sources and it varies seasonally;being highest in the
summer and lowest in the winter.This is a direct result of the
spring snowmelt and summer rainfall which recharge aquifers and raise
the water table level,and depletion of the aquifers in the winter due
to lack of recharge.The regional groundwater component appears to be
the second most important source of subsurface flow which remains
relatively constant throughout the year because the down valley
gradient of the flood plain is constant.
IV-16
-
r:
I
Relationships between slough flow and mainstem flow (when the berms
are not overtopped)indicate that infiltration from the mainstem
varies nearly linearly with the mainstem stage.In general,a one
foot change in mainstem stage results in a change in slough f10w,of
between 0.3 and 0.6 cfs depending upon the particular side slough
(APA 1984b).Relative to normal slough flows which are 3 to 5 cfs the
influence of mainstem infiltration on open channel hydraulic
conditions within the slough are minor.However,this small change in
slough flow appears to have a significant effect on the biologic
processes occurring within the streambed of the slough;particularly
during fall and early winter.
Seasonal changes in the mainstem water surface elevation also effect
the rate of infiltration or intragravel flows from the mainstem.The
annual cycle of mainstem water levels includes two extended periods of
relatively constant water surface elevation and two brief transition
peri ods.The two extended peri ods are mi d-May through mi d-September
and the winter season from December through April.The two transition
periods are breakup which generally occurs during the first two weeks
of May,and the October-November freeze-up period.The mainstem water
levels are highest during the two extended periods and lowest during
the October-November freeze-up period.
Middle Susitna River streamflows normally reach 20,000 cfs by the end
of May and remain at that level or higher until mid-September.
Throughout this period,bank storage and infiltration of mainstem
water to the sloughs fluctuates in response to mainstem water levels.
Between late September and mid-November,mainstem streamflow often
dec1 ines to 4000 cfs prior to an ice cover forming on the mainstem.
Depending on the reach of the river being considered,the difference
in mainstem water surface elevations between streamflows of 20,000 and
4,000 cfs would approximate 5 feet.
The mainstem water levels associated with October and November
streamflows appear to result in the lowest infiltration flows and
IV-I?
slough flows for the year.During this period,when discharges range
from 5,000 to 3,000 cfs,upwelling flow is thought to originate almost
ent ire ly from the regi ona 1 groundwater component.Ma i nstem stage is
too low to significantly contribute to infiltration and cold air
temperatures have retarded subsurface flow from upland sources.
As the ice cover forms on the river,the mainstem water level rises in
response to the blockage of streamflow by river ice.This natural
process of raising mainstem water surface elevations upstream of the
ice cover is called Il s taging ll
•Because of staging,mainstem water
levels during winter (December through April)appear similar to those
of summer water levels (Trihey 1982).Hence,infiltration from the
mainstem into side channel and slough areas during winter is suspected
of being similar to that of summer.
In general,intragravel temperatures at upwelling areas remain between
2.5 and 4°C throughout the year (Estes and Vincent-Lang 1984b;Keklak
and Quane 1985).This temperature range approximates the mean annual
temperature of the Susitna River.Intragravel temperatures in side
sloughs are relatively insensitive to surface water temperatures when
the upstream berm of the slough is not overtopped by mainstem flow.
However,when the upstream berm of a side slough or side channel is
overtopped by rna i nstem flow,intragravel temperatures may be
infl uenced.Thi sis most evi dent du ri ng freeze-up when i ntragrave 1
temperatures are sometimes depressed to near DOC in response to the
inflow of cold mainstem water caused by staging {see ice processes).
Overtopping events during freezeup do not occur at all side sloughs.
However,they appear to be more common downstream of River Mile 130
than upstream of this location.
Biological Importance of Upwelling
Intragravel flow and upwel1 i ng are two of the most important habitat
variables influencing the selection of spawning sites by chum and
sockeye salmon in the middle Susitna River (Estes and Vincent-Lang
I984d).In addition,upwel1ing flows contribute to local flow in
IV-18
-
-
......
-
-
-
sloughs and side channels which may occasionally facilitate fish
passage (Estes and Vincent-Lang 1984c).
Incubation appears to be the life stage most critically affected by
intragravel flow in the middle Susitna River.Chum and sockeye salmon
embryos spawned in areas of upwelling flows benefit if intragravel
flow continues throughout the winter.The 2 to 4°C intragravel
temperature associated with upwellings in side sloughs maintains a
higher rate of survival for the incubation of embryos than do
intragravel temperatures in other habitats (Vining et al.1985).
Intragravel flow is also thought to ensure the oxygenation of embryos
and alevins,transport metabolites out of the incubating environment,
and inhibit the clogging of streambed material by fine sediments.
Groundwater also appears to be an important factor i nfl uenci ng the
Itllinter distribution of juvenile salmon and resident fish (Roth and
Stratton 1985;Sundet and Pechek 1985).Upwelling flows may comprise
the predominant source of water in sloughs when overland runoff from
precipitation is inhibited due to freezing.This constant water flow
in sloughs and side channels provides over-winter habitat for juvenile
sockeye,chinook,and coho salmon and resident species.The warmer
temperatures of sloughs and side channels due to the inflow of upland
source and bank stored groundwater apparently attract overwi nteri ng
fish and may reduce their winter mortality (Dugan et al.1984).
As previously stated,upwelling flows appear to reach their annual
minimum during late October and November prior to an ice cover forming'
on the ma i nstem.Intragravel temperatures (upwell i ng rates)during
this period probably limit the incubation success of embryos that were
spawned when upwelling rates were higher.As a result of decreased
upwelling rates during the October-November period many embryos are
thought to be dewatered or frozen.The most viable incubation habitat
in the middle Susitna River is thought to exist where upwelling flow
persists during this fall transition period.
IV-19
Maintaining higher than natural mainstem discnarges during the fall
transition would likely increase upwelling rates above natural levels,
thereby i ncreasi ng the incubation success in the effected spawni ng
habitats.Reducing mainstem discharge to below natural levels would
likely have an opposite effect on incubation success.
IV-20
-
-
-
-
-
Sediment Transport Processes
Sediment transport is defined as the movement of inorganic material
p'ist a particular point in a stream.The total sediment load consists
of suspended load and bed load.Suspended load includes wash load,
fine material constantly in suspension,and coarser materials
transported through intermittent suspension.The bed load consists of
all inorganic material moving in constant contact with the streambed.
1"""
I
It is well-documented that sediment transport processes have a
si gnifi cant i nfl uence on aquati c habitat.McNeil (1965)has observed
that streambed stabil ity can i nfl uence the success of sal moni d egg
incubation.Several researchers have shown that substrate composition
influences the survival of eggs to fry in salmonid populations (McNeil
and Ahnell 1964;Cooper 1965;McNeil 1965;Phillips et al.1975).The
suitabil ity of a streambed for rearing fish and aquatic insects is
also influenced by its stability composition.
r
-
-
On a macrohabitat level,the channels of the middle Susitna River are
quite stable given the range of streamflows and ice conditions to
which they are subjected.Review of aerial photography taken over an
approximate 35 year period (from 1949-51 to 1977-80)indicates that
the plan form of the middle Susitna River has experienced 1ittle
change (Univ.of Alaska,AEIDC 1985b).Although there is some
evidence of degradation,and some peripheral areas have changed from
one habitat type to another,the plan form of most channels appear
unchanged over this period.
The plan form of the middle Susitna River appears to be controlled by
geologic features and major floods 'but is also influenced by ice
processes.Stream channel size and streambed composition are
primarily the result of hydrologic processes.Flood events are
probab ly the dominant channel formi ng process whereas norma 1 summer
streamflows represent the primary sediment transport process.Channel
forming discharges are rare;occurring perhaps once or twice within a
IV-21
---,--,....,----_._----------------------------_......
25-to 50-year period (refer Table IV-3).High streamflows,such as
the bankfull discharge or 5-year flood might reshape the channel
geometry to reflect local hydraulic conditions but have little
influence on the overall plan form of the middle Susitna River.
River ice can also influence the plan form of the river by causing ice
jams during breakup which divert large quantities of water from
primary channels into secondary channels or onto the floodplain
forming new channels.Velocities near 10 ft/sec have been measured at
constricted areas within ice jams (R&M 1984b).Such velocities have
the potential to cause significant local scour.When ice jams fail
they release a surge of water and ice which was impounded behind the
jam.These surges contain high velocities that erode streambanks,and
ice blocks carried in the surge wave often scour banks and knock over
vegetation (R&M 1984b).Bank erosion by ice-block abrasion is
extensive in some locales of the middle Susitna River (Knott and
Li pscomb 1983).
Shore ice forms along the streambanks prior to the upstream
progression of the ice cover.This ice may freeze onto the bank
material and around vegetation.When the water level rises due to
stagi ng associ ated wi th the ice cover formation the shore ice may
break off from the shoreline carrying bank materials and vegetation
with it.The amount of sediment transported by shore ice is
insignificant when compared to other transport mechanisms.However,
shore ice processes expose the shore 1 i ne to scour by floods and
significantly influence the character of fish habitat along the
channel margin by removing debris jams and other types of shoreline
cover.
IV-22
-
-,
-
-
"""!,,
-
-
Influence of Sediment Transport Processes on Habitat Types
A streambed which is in a long term state of sediment equilibrium is
generally relatively stable when streamflows are at or below flood
ll:vels,but may degrade during a flood and aggrade as the flood peak
subsides.The mainstem and large side channels of the middle Susitna
River appear to reflect this type of dynamic equil ibrium based upon
streambed measurements by the U.S.Geological Survey at Gold Creek
(Fig.IV-6).
Slediment transport processes exert varying degrees of influence on the
streambed composition of the six aquatic habitat types (mainstem,side
channels,side sloughs,upland sloughs and tributaries)within the
middle Susitna River (Tables IV-5 and IV-6).
Table IV-5.Influence of mainstem sediment load on streambed com-
position of aquatic habitat types.
-
Habitat Type Suspended Load Bedload
Mainstem and Large
Side Channels
Side Channels
Side Sloughs
Tri buta ry Mouths
Upland Sloughs
Primary Primary
Primary Secondary
Primary t4i nor
Minor Secondary
Secondary Minor
Mainstem and Large Side Channel Habitats
Summer streamflows transport large amounts of sand both in suspension
and as bedload.Streambed materials in the mainstem and large side
channels generally range from large gravels «3 inches)to cobbles
«10 inches).Streambed materials in the smaller side channels
generally range from large gravels to small cobbles (6 inches).Bed
IV-23
-------_........._---------....,..----------------------
SUSITNA
AT
RIVER CROSS SECTIONS
GOLD CREEK
RIGHT BANK
/
I
I
/
400
..
o
I
I
I
"I1-/
1
I
\ 1
\ 1
\ I,
200 'I
WIDTH (feet)
June 3,1964 ( 6 tI,100 ch)
prior to flood peok ( 3 doy.I
- - -July 14,1964 (28,200 chI
ofter peok event
o 0 June 10,1971 (50,000 etl)
........MAY 3,1984 (12,600 etll
\00
o
LEFT BANK
o
o
I~
10
--CD
CD........
t-
.......
J:
<
C)
I
N
W
..j::>
J:5
w
C)
<C)
Figure IV-5.Cross sections of the Susitna River at Gold Creek measured at various
mainstem discharges.
J J J )J i l J 5 ,)J J
1 1 1 )1 ~····-·l ~-1 1 1 -))
Typical ICe Jam
High Flow Midsummer Surges and
Events Discharge Diverted Flow
Mainstem and
Large Side Channels Primary Insignificant Secondary
Side Channels Primary Minor Primary
Side Sloughs Primary Minor Primary
Tributary Mouths Primary Insignificant Minor
Upland Sloughs Minor Ins i gnifi cant Insignificant
......
<
I
N
Ul
Table iV-G.Influence of sediment transport processes on streambed stability of aquatic habitat types.
Mechanical
Scour by Anchor Ice Shore Ice
Ice Blocks Processes Processes
Secondary Minor Secondary
Minor Minor Secondary
Insignificant Insignificant Insignificant
Insignificant Minor Ins i gnifi cant
Insignificant Insi gnffi cant Insignificant
,
material sizes are largest near Devil Canyon and generally decrease
with distance downstream (Bredthauer and Drage 1982).
Beneath this surface layer is a more heterogenous mixture of material
consisting of sands and gravels with some cobbles.Under normal flow
conditi ons the overlyi ng 1ayer of cobbles protects the underlyi ng
streambed material from erosion.The ability of this pavement layer
to resist erosion is enhanced by the deposition of fine glacial sands
within the interstitial spaces between the rubble and cobble.This
results in a tightly packed matrix of sands,gravels and cobbles.The
fine sands which fill the interstitial spaces within the pavement
layer are a part of the suspended sediment load normally transported
by summer streamflows.
Except for isolated deposits of sands and gravels~streambed material
in the mainstem and large side channels appears sufficient to resist
eros i on or transport by streamflows 1ess than 35,000 cfs.Flood
events (50,000 cfs or greater)have the capacity to erode the pavement
layer and transport underlying streambed materials downstream.As the
flood crest recedes the large bed elements in motion are redeposited,
thereby reformi ng the protective pavement 1ayer whil e sands and
gravels are transported downstream.As a result the streambed
elevation decreases while retaining much of the basic plan form of the
river.Evidence of such long-term channel degradation has been
documented through analysis of aerial photography (Univ.of Alaska,
AEIDC 1985b;Klinger and Trihey 1984;Klinger-Kingsley 1985).
River ice influence the shape and character of mainstem and large side
channel habitats in several ways:1)scour caused by ice jams during
breakup,2)sed"iment transport by anchor ice and possibly by frazil
ice,and 3)scour and sediment transport by shore ice.In comparison
to sediment transport associated with high streamflows,scour by ice
jams,is of secondary importance.The volumes of sediment transported
in the middle Susitna River by anchor ice and shore,are inconse-
quential.However,the influence of shore ice on streambank vege-
tation and cover objects for fish appears to be significant.
IV-26
...,
-
-
-
.....
Side Channel and Side Slough Habitats
Of the sediment transport processes described in the previous section,
high flows and flooding caused by ice jams during breakup have a
dominant role in the formation and maintenance of side sloughs and
side channels.Mechanical scour by block ice,anchor ice processes,
and shore ice processes have little influence on substrate composition
or streambed stability in these habitats.
Side channels and side sloughs are quite stable when conveying typical
mid-summer streamflows.Their width to depth ratios and spatial
orientation indicate they were formed by much higher streamflows.
Although the temporal frequency of such high flows varies between
sites in accord with the breaching flow,it is generally low;
occurring perhaps once or twice within a 25-year period.
New channels have also been formed as a result of ice jams which raise
the mainstem water level and cause flow to be diverted onto the flood
plain.Slough 11,for example,was changed from an upland slough to a
side slough in 1976 when an ice jam occurred below the Gold Creek
ra-Ilroad bridge.However,ice jam diversions are generally more
important for maintaining substrate quality in side slough habitats by
flushing out fine sediments,as observed at Slough 9 during May 1982.
Sediment is transported into side sloughs and side channels from three
sources:1)the mainstem,2)tributaries,and 3)bank erosion.Of
these,the mainstem influence is most significant.Large quantities
of suspended sand and smaller sediments are transported into side
channel and side slough habitats when the mainstem discharge is
sufficient to overtop their upstream berms.Summer streamflows in the
range of 20,000 to 30,000 cfs cause significant siltation of pools and
backwater areas associated with side channel and side slough habitats.
IV-27
-----------------------------------------------
Tributary and Tributary Mouth Habitats
High flow events are most important for shaping the channel geometry
and determining streambed composition of tributary mouths.Most
tributaries to the middle Susitna River are small,steep gradient
streams with a capacity to transport large quantities of bed load
during flood events.
When flood events are caused by regional rainstorms,the Susitna River
would have a high discharge concurrent with,or soon after,the high
di scharge in the tributary.As a result,most sediments del ivered to
the tributary mouth by the tributary are transported downstream by the
Susitna River.However,local storms may cause a .tributary to flood
while the Susitna River remains relatively low.In such cases,a
delta may build up at the mouth of the tributary due to the deposition
of the tributary bed load.The delta may extend into the Susitna
River until subsequent streamflowsin the river are·sufficient to
erode it and transport the material downstream.This process has been
periodically observed at the mouths of Gold Creek and Sherman Creek.
Upland Slough Habitats
In general,upland slough habitats are isolated from mainstem sediment
transport processes.However,an exception exists in the vicinity of
the slough mouth,where sediment laden mainstem flow often enters the
slough as backwater during periods of high mainstem discharge.The
suspended sediments contained in the mainstem flow settle out in these
low velocity backwater areas and contribute to the long term
sedimentation of the slough.If a backwater eddy occurs,as at the
mouth of Slough 10,sedimentation of the slough mouth and its
downstream approach can be caused by only two or three moderately high
flow events.In other instances such as Slough 6A where ma i nstem
water has some difficulty entering the slough mouth,sedimentation is
more subtl e.
IV-28
-
-
-
....,
-I
-
-
Project Influence on Sediment Transport Processes
Construction and operation of Watana Reservoir will alter the natural
streamflow,thermal,and sediment regimes of the middle Susitna River.
Flood discharges in the middle Susitna River will be smaller in
.magnitude and will occur less frequently (refer Table IV-3).In
clddition most suspended material and all bed load originating upstream
of the dam sites will be deposited in the reservoirs (R&M Consultants
1982d;Ha rza-Ebasco 1984e).Hence,the amount of sediment currently
being transported through the middle Susitna will be substantially
r'educed.
The smaller and less frequent flood flows which would occur are
expected to favor streambed and streambank stabil ity in ma i nstem and
side channel habitats.Reduced flood peaks al so favor the
encroachment of streambank vegetation into side sloughs and on exposed
portions of partially vegetated gravel bars.In addition,smaller and
les's frequent flood events should allow tributary deltas to enlarge
over their natural size.Some tributary mouths may become perched but
most are expected to adjust themselves to with-project water level s
(R&M 1983b).Gravel depos its are expected to occur in rna i nstem and
side channel areas immediately downstream of most tributaries being
Ulsed by spawning salmon.Access into these tributaries by adult
salmon is not expected to be impaired by with-project changes in
tributary deltas (Trihey J983).
Because most sediments entering Watana Reservoi r wi 11 be trapped,a
tendency will exist for fine sediments to be removed from the stream-
bed downstream of the dam.Although peak flood events wi 11 be sub-
stantially reduced by the reservoirs,regulated flood discharges at
the Gold Creek gage will often be in the range of 30,000 to 40,000 cfs
(refer Table IV-3).Gravel and smaller sediments are expected to be
dislodged from the streambed by these flows and transported
downstream.Since the dislodged material will not be replaced as it
is under natural conditions,some accelerated degradation of the main
channel bed should be expected.
IV-29
-----,---------------................-------.......----------
Whil e the actual amount of degradati on whi ch woul d occur cannot be
accurately forecast,analysis of bed material samples and inspection
of exposed portions of the streambed during periods of low streamflow
indicates that degradation of the main channel should not exceed one
foot (Harza-Ebasco 1985e).Degradation would be greatest near the dam
face and is expected to decrease with distance downstream.In time,a
pavement layer would develop due to removal of the smaller bed
materials which would retard any further degradation.This layer will
consist of a smaller percentage of fines and a greater percentage of
voids than occurs naturally.
The influence that with-project ice processes might have on channel
stabil ity will,in part,depend upon project design and operation.
The effects of alternative intake level design and winter operating
policies on downstream ice processes have been evaluated by
Harza-Ebasco (1985d)and are summarized in a following section of this
report called II I nstream Temperature and Ice Processes.11 For the
purpose of discussing with-project ice effects on channel stabil ity
and sediment transport processes,it is sufficient to say that only a
portion of the middle Susitna is expected to be ice covered.
The with-project ice cover is expected to melt in place rather than
break up under hydraul ic pressure as it presently does.Breakup ice
jams are expected to occur less frequently,if at all,and be of
reduced magnitude (Ha rza-Ebasco 1985d).Thi sis expected to reduce
the influence of the river ice cover on naturally occurring sediment
transport processes.However,maximum ice cover elevations within the
ice-covered portion of the river are expected to be several feet
higher than natural during operation of stages I,II and III
(Harza-Ebasco 1985d).Thus disturbance of shorel ine vegetation and
the potential for streambank erosion within the ice covered portion of
the middle Susitna is expected to increase above present levels.
Upstream of the ice front,shoreline disturbances by shore ice pro-
cesses would not be expected to change appreciably.The shore ice
IV-3D
""'"
-
-
-
.-
that woul d form upstream of the ice cover is expected to occur at an
elevation below the present veget~tion level.Melt out in spring is
i:xpected to reduce the frequency of shore ice separating from the
streambank and floating downstream (as with natural breakup)with
l:ncased debri sand vegetation.Hence,streambanks shou 1d be 1ess
prone to erode.
IV-31
Instream Water Quality and Limnology
Baseline Condition
Water quality encompasses numerous physical and chemical characteris-
tics,including the temperature,density,conductivity,and clarity of
the water,as well as the composition and concentration of all the
dissolved and particulate matter it contains.Water quality influences
the quality of fish habitat by virtue of its direct effects on fish
physiology and because it largely governs the type and amount of
aquatic food organisms available to support fish growth.
Each of the aquatic habitat types associated with the middle Susitna
River differs not only in terms of its morphology and hydraulics,but
also in the basic pattern of its water quality regime.Therefore,the
relative importance of a specific habitat type to fish may change in
response to seasonal change in either streamflow or water quality.In
the middle Susitna River,turbidity is an influential and visually
detectable water quality parameter that may be used to classify the
six aquatic habitat type.s into two distinct groups during the open
water season;clear water or turbid water.In order to gain a
greater understanding of each habitat type,it is useful to 1)examine
the water quality characteristics of both clear and turbid water
aquatic habitats;2)identify how the water quality of these aquatic
habitat types changes on a seasonal basis;and 3)determine how these
seasonal changes influence the quality of the aquatic habitat types.
From June to September highly turbid water accounts for the greatest
amount of wetted surface area in the middle Susitna River (Klinger and
Trihey 1984).During this period,when surface runoff and glacial
melting are greatest,total dissolved solids,conductivity,
alkalinity,hardness,pH,and the concentrations of the dominant
anions and most cations tend to be at their lowest levels of the year,
while stream temperature,turbidity,true color,chemical oxygen
demand,total suspended solids,total phosphorus,and the total
IV-32
~,
-
-
-
~,
-
-
c:oncentrations of a variety of trace metals are at their highest
va 1ues for the year (Table IV-7).Average nitrate-ni trogen concen-
trations remain relatively constant throughout the year with greater
variation during the summer as discharge fluctuates.
The basic water chemistry of the clear water flow of the middle
Susitna River in winter,and of certain groundwater fed habitat types
throughout the year,can be generalized from an evaluation of the
~Iater qual ity record for the Susitna River at Gold Creek during
winter.Surface water flow throughout the basin is low.Middle
Susitna River discharge is comprised almost entirely of outflow from
the Tyone River System (lakes Louise,Susitna,and Tyone)and
Sjroundwater inflow to tributaries and the mainstem itself.Hence,the
c:oncentration of suspended sediment,trace metals,and phosphorous is
also low or below detection limits.Groundwater spends a greater
olmount of time in contact with the soil and underlying rocks of the
watershed than surface runoff or gl aci a1 meltwater and thus contains
more dissolved substances.Groundwater temperatures are warmer in
\iltinter and cooler in summer than surface water temperatures.
The specific water quality characteristics of clear or turbid water
flowing through a given channel may differ from the general
descriptions provided above,depending on local variations in the
<Jlffiount of local surface runoff or the composition and distribution of
Y'ocks,soils,and vegetation.Nonetheless,a generalized seasonal
water qual ity regime unique to each habitat type seems to prevail,and
having knowledge of it provides useful insight into the direct and
indirect role water quality plays as a component of fish habitat
within the Talkeetna to Devil Canyon segment of the Susitna River.
IV-33
Table IV-7.Mean baseline water quality characteristics for middle Susitna
River at Gold Creek under (a)turbid summer (June-August)
conditions and (b)clear,winter (November-April)conditions
(from Alaska Power Authority 1983b).
Parameter Units of Turbi d Cl ear
(Symbol or Abbreviation)Measure (summer)(Wi nter)
Total Suspended Solids (TSS)mg/l 700 5
Turbi dity NTU 200 <1
Total Dissolved Solids (TDS)mg/l 1 90 150
Conductivity (~mhos cm-,25°C)145 240
pH pH units 7.3 7.5
A1ka 1i nity mg/l as CaC0 3 50 73
Hardness mg/l as CaC0 3 62 96
Sulfate (SO -2)mg/l 14 20
Chloride (Ci)+2 mg/l 5.6 22
Dissolved Calcium (Ca ~2 mg/l 19 29
Dissolved ~agnesium (Mg mg/l 3.0 5.5
Sodium (Na ) +
mg/l 4.2 11.5
Dissolved Potassium (K )mg/l 2.2 2.2
Dissolved Oxygen (DO)mg/l 11.5 13.9 ~
DO (%Saturation)%102 98.0
Chemical Oxygen Demand (COD)mg/l 11 9
Total Organic Carbon (TOC)mg/l 2.5 2.2
True Color pcu 15 5
Total Phosphorous ~g/l 120 30
Nitrate-nitrogen as N (N0 3-N)mg/l 0.15 0.15
Total Recoverable Cadmium '"""I
[Cd(t)]~g/l 2.0 <1
Total Recoverable Copper
[Cu(t)]~g/l 70 <5 """\
Total Recoverable I ron
[Fe(t)]~g/l 14,000 <100
Total Recoverable Lead
[Pb(t)]~g/l 55 <10
Total Recoverable Mercury
[Hg(t)]~g/l 0.30 0.10
Total Recoverable Ni eke 1
[Ni (t)]~g/l 30 2
Total Recoverable Zinc
[Zn(t)]~g/l 70 10 ~
IV-34
-
Effects of Water Quality on Habitat Types
Mainstem and Side Channel Habitats
A comparison of the summer and winter water qual ity record for the
Susitna River at Gold Creek (refer Table IV-7)reveals a seasonal
contrast in the water qual ity conditions of the mainstem and its as-
sociated side channels.During winter almost all the flowing w~ter is
covered with ice and snow.However,high velocity areas in the
mainstem and small isolated areas of warm (3-4°C)upwelling
!~roundwater maintain scattered open leads in side sloughs and some
side channels.During late March and April open leads begin to appear
where groundwater occurs along mainstem and side channel margins or at
mid-channel islands and gravel bars.A winter-spring transition algal
bloom probably occurs at these open leads prior to breakup in mid-May.
During May (spring breakup)stream flow rapidly increases from
approximately 2,000 cfs to 20,000 cfs or greater.Suspended sediment
concentrations fluctuate considerably (9 -1,670 mg/l),but average
approximately 360 mg/l (Peratrovich et ale 1982).Most of the benthic
production that occurred during the winter-spring transition is likely
dislodged and swept downstream.A portion of this material may follow
the natural flow path along the mainstem margin and into peripheral
side channels and sloughs.Thus high spring flows may redistribute
fish food organisms and some of the organic production associated with
the winter-spring transition.At prevail ing springtime turbidities
(50 to 100 NTU),the euphotic zone is estimated to extend to an
average depth of between 1.2 and 3.5 ft (Van Nieuwenhuyse 1984).
Hence,the mainstem margin and side channels is capable of supporting
a low to moderate level of primary production wherever velocity is not
'1 imiting.In summer,mainstem turbidities increase to approximately
;~OO NTU and 1 imit the total surface area available for primary
production by reducing the depth of useful 1ight penetration to less
than 0.5 ft (Van Nieuwenhuyse 1984).
IV-35
La rge ly because of its water quality (especi ally its hi gh suspended
.sediment concentration),high velocities and large substrate,the
principal function of mainstem habitat during the summer months is to
provide a transportation corridor for inmigrating spawning salmon and
olJtmigrating smolts.Mainstem water quality also has a significant
influence on the seasonal water quality regime of side slough habitats
when overtopping of side slough occurS.
Field observations made in 1984 by EWT&A suggested that during the
autumn transition period,a second pul se of primary production may
occur in the mainstem and side channel habitats.The Fall pulse
appears,dominated by green filamentous algae rather than diatoms.
This second bloom,induced by moderating stream flows and a notable
reduction in turbidity levels to less than 20 NTU,probably exceeds
the winter-spring transition bloom in terms of surface area affected
and biomass produced.This fall-winter bloom probably stops with the
onset of freezeup.Hence in some years,as in 1984,the autumn
transition may span eight to ten weeks and the primary production can
be significant,while in other years,such as 1983,freezeup can occur
within three to four weeks after the river begins to clear.
Side Slough Habitats
Side sloughs present a unique seasonal pattern of streamflow and water
quality that is important to many fish species inhabiting the middle
Susitna River.The most significant changes in side slough water
quality are associated with their periodic overtopping by mainstem
discharge that temporarily transforms the clear water side slough
habitat into turbid water side channel habitat.During each
overtopping event,the side slough water quality and temperature are
dominated by the prevailing characteristics of the mainstem.
Overtopping during summer generally causes an increase in turbidity
from zero to near 200 NTU and a temperature increase from 6°e to 10 or
12°C.Overtopping during winter has little effect on turbidity but
reduces surface and intragravel water temperatures from 3°e to zero.
IV-36
~,
-
r
i
-
-
.-
-
Field observations by EWT&A suggest that some of the sediment carried
through sloughs seems to become part of an organic matrix of unknown
composition (probably involving bacteria,fungi,and other microbes)
which in turn is usually covered by a layer of pennate diatoms and/or
colonial and filamentous algae.This benthic community,which covers
most streambed material greater than 2 to 3 inches in diameter,can be
observed throughout the middle Susitna River in mainstem and side
channel habitats as well.It is possible that the phosphorus
associated with the sediment plays some role in supporting the organic
matrix and studies (Stanford,Univ.of Montana,pers.comm.1984)
elsewhere indicate that as much as 6 percent or more of this
sediment-bound total phosphorus can become bio 1ogi ca lly avail ab 1e --
perhaps to the diatoms.This might help explain how primary producers
can still maintain a viable presence even under short-term highly
turbid conditions.
During late September and early October 1984,fall-winter transitional
algal blooms wer~observed by EWT&A in most side sloughs and are
suspected to occur every year.The 1984 bloom was characterized by
dense mats of filamentous green a19ae growing on submerged streambed
materials one inch in diameter and larger.
In winter,side slough discharge is often ma'intained by numerous
9roundwater upwell ings which generally range between 2°and 4°C.
During winter upwelling areas often maintain open leads in the ice
cover and they provi de intragrave 1 habitat for i ncuba ti ng embryos and
overwi nteri ng opportuni ti es for juvenil e anadromous and res i dent fi sh
(ADF&G,Su Hydro 1983c).
During the winter-spring transition period (late March to mid-May)
side slough surface water temperatures exceed intragravel water
temperatures during portions of the day but are cooler than
i ntragravel temperatures duri ng the ni ght (Tri hey 1982;ADF&G,Su
Hydro 1983a).Primary production rates probably increase at this
time.Chum,sockeye and pink fry emerge from natal areas within the
IV-37
--_.~-------------------------------------
sloughs during this transition period and can be observed swimming and
feeding in quiescent pools during the warm portions of the day.
During the remainder of the day the fry appear to have burrowed into
the streambed.
Upland Slough Habitats
Upland slough habitat is distinguished from side slough habitat by the
1ack of overtoppi ng of the upstream slough end by hi gh rna i nstem
discharges.Groundwater upwelling and local runoff dominate the water
quality characteristics of these habitats and turbidities are
typically less than 5 NTU throughout the year.Surface and intra-
gravel water temperatures are similar to side sloughs.The slough
mouths are influenced by turbid backwater effects from the mainstem.
Tributary and Tributary Mouth Habitats
The seasonal water quality pattern displayed by the tributar,ies is
closely 1inked to their annual flow regimes.This pattern is of
considerable interest since it is in the tributaries--most notab1y
Portage Creek,Indian River,and Fourth of July Creek--where most of
the fi sh producti on for the mi ddl e Sus itna Ri ver ori gi nates (ADF&G
1981;ADF&G,Su Hydro 1982b;Barrett et al.1984).These streams
provi de spawni ng,reari ng,and overwi nteri ng habitat that either does
not exist,or only exists in limited amounts in other habitat types.
Tributaries,in effect,represent the most productive of the aquatic
habitats in the middleSusitna River.Thus,although not influenced
by the Susitna River streamflow or water quality regimes,valuable
ins i ght can be gained by understandi ng s imil ariti es and differences
between the water qua1ity of the tributaries and the Susitna River.
The ionic composition of tributary water 1 ikely conforms to the
hydrologic principle that the soils of a stream basin genera1ly govern
the quantity and the quality of the solids contained in the water
flowing from it.The moderate concentrations of macronutrients
IV-38
~I
""'"
""'ii
'"""'
-~
(phosphorus and nitrogen)that prevail in these streams probably
represent only that which leaks from the internal cycling taking place
'in the soils of the local watershed.Although production levels are
thought to be determined by water quality,variations in productivity
levels within these tributaries are probably due more to hydraulic and
hydrologic conditions than to water quality.
In winter,tributary flow is minimal and is predominantly comprised of
!~roundwater rising up through the bed of the stream channel.Since
much of the winter mainstem flow is comprised of contributions made by
!~roundwater and tributa ry sources,tri butary water chemi stry is
probably reflected in the winter water chemistry characteristics of
the mainstem (refer Table IV-7).Thus,the water quality
characteristics of tributaries during winter reflect a well-buffered,
\vell-oxygenated envi ronment for embryo incubation and adult and
juvenile overwintering.
During the April-May transition between winter and the onset of spring
runoff,porti ons of the ice and snow cover on the tri butary melt away.
\~ater temperatures may increase sl ightly and a pul se of primary
producti on probably occurs in response to a lengtheni ng photoperi od
(Hynes 1970).The ability of light to reach the algal community is
assi sted by the absence of 1eaf cover on stream bank vegetati on and
by the presence of rotten ice that effectively transmits light
(LaPerriere,Univ.of Alaska,pers.comm.1984).The emergence of
some fish species and many insects is apparently timed to occur during
this brief early-spring transition.
By mid-May air temperatures in the middle Susitna have increased to
goC and spring runoff from melting snow has filled the tributary
channel.Spring flooding generally causes redistribution of portions
of the streambed,displacement of fish from overwintering habitat,and
the flushing of organic and inorganic debris,as well as much of the
benthic community from the stream (Hynes 1970).This erosion causes
an increase in suspended sediment concentration and turbidity.
Likewise,color,total organic carbon,and chemical oxygen demand
IV-39
---,---------------------------------------
increase substantially,while the inflow of surface runoff dilutes
winter concentrations of dissolved solids.It is likely that the
spring freshet serves as a functional reset mechanism for the system;
cleansing it in preparation for the sequence of ecological events to
follow.
Summer is the season when juvenile fish are most active.Typical
water quality in tributaries during the summer (June to mid-September)
probably approximates the winter condition except for lesser concen-
trati ons of di ssol ved sol ids and wa rmer stream temperatures whi ch
fluctuate diurnally.Rearing is supported primarily by the growth and
recruitment taki ng place withi n the aquatic insect community
(especially chironomids).The carrying capacity of tributaries,
however,does not appear adequate to support the large numbers of
rearing juveniles,so many juveniles outmigrate at this time to
continue their development elsewhere (Dugan et ale 1984).
During late September and early October a second transition period
occurs as streamflow,photoperiod,and temperature gradually decline.
Algal biomass and productivity are probably at their annual peak
during this time,as is the standing crop of benthic macro-
invertebrates (Hynes 1970).This algal mat is not only a food source
for a variety of insect larvae and nymphs,but also serves as
microhabitat for many aquatic organisms including juvenile fish.The
leaves shed from riparian vegetation may provide further microhabitat
and insect food substrate.
By late October,surface water temperatures are aoe and an ice cover
begins to form.Unstable border ice and anchor ice probably dislodge
a substantial portion of the benthic community,causing it to be swept
downstream.Much of what remains of this community may be frozen in
place as the ice cover formation continues.Freezeup is usually
complete by late November or early December when the winter phase of
the annual cycle begins once again.
IV-40
"""1,
"""
.....
-
r
L
-
With-Project Relationships
Seasona 1 stream temperatures,suspended sediment concentrati ons and
turbidities influence the qual ity of aquatic habitat types in the
middle Susitna River,and therefore are important to the distribution
and production of fish.It is also evident that these water quality
parameters will be more di rectly affected by constructi on and opera-
tion of the proposed project than will other water qual ity parameters
(Peratrovich et al.1982;Univ.of Alaska,AEIDC 1985a).The
foll owi ng di scussion focuses on wi th-project re 1ati onshi ps between
suspended sediment and turbi dity.Stream temperature is di scussed in
the following section of this report.
The suspended sediment regime of the Sus itna Ri ver downstream of the
impoundments will change significantly as a result of project
construction.Project operation is thought to have a minor influence
on downstream suspended sediment concentrations.The reservoir(s)is
estimated to trap between 70 and 98 percent of the total vol LIme of
sediments that are annually transported through the middle Susitna
River (R&M 1982d;Harza-Ehasco 1984e).Very fine sediment particles
«5]1 in diameter)will remain in suspension year round within the
reservoirs (APA 1983b).These small particles create a turbidity far
greater in proportion to their mass than do larger particles.
Estimates for the expected concentration of total suspended sol ids
released year round from the reservoir (s)range from 0 to 345 mg/l,
"'lith the expected average to range between 30 and 200 mg/l
(Peratrovich et al.1982)~More recent estimates (Harza-Ebasco 1985e)
"iindicate that suspended sediment concentrati ons in the outflow from
Watana Reservoir during the year would range between 3d and 130 mg/l
for stages I and II,and between 10 and 80 mg/l duri ng the year for
stage III.
Although a relationship between total suspended solids.(TSS)and
turbidity (NTU)is difficult to define,settling column studies of
Susitna River water indicate that turbidity (NTU)is approximately
IV-41
twice the suspended sediment concentration (mg!l)(R&M 1984c).Lloyd
(1985)has also compiled a relationship between turbidity and
suspended sediment concentrations using data from several glacial
streams in Alaska (Fig.IV-n.Unfortunately,an order of magnitude
difference in turbidity is calculated for the same suspended sediment
concentration using these relationships (Table IV-8).To date,
insufficient information is available to determine which of these
relationships is more applicable to project conditions.
However,a relationship between turbidity (NTU)and compensation depth
(feet)developed by Van Nieuwenhuyse (1984)indicates the depth to
which photoactive radiation might penetrate the middle Susitna River
under a broad range of turbidities (Fig.IV-8).Evaluation of
with-project turbidity and streamflow levels on the euphotic surface
area of the middle Susitna River is in progress (Reub·et al.1985).
TURBIOITI (['!TV l.
-
""",!,
::c
I-
fu =Cl
.j
9
200 ~oo leoo
....
Figure IV-8.Theoretical curve of turbidity versus compensation
depth (Reub et al.1985).
IV-42
-
::::I....100z
,.......e
iii
0::
::::I
l-10-
I
•
••
I
"'
,
•
•
•
• •,,"$••
I..• •••••••..,....,.-....,..I...."• •."
yl .0 'I "•e....••••.~....
•
•
•••:"
I
•
•
,
A,•
•
•••••.~:
•••e·•."••
•
•
•
••-...
•
••
I
·•
T.0.44(SSC)0.858
~.0.83
n =229
1000
I~OOO
...
,
•••
10,000100010010
.I'----L.......L-..L..J.J-U..L.l.----'---.L.-..L..J...L..1J.JU----L-J-...I..-L.u..Ll...1.---L--L.....L...L..L...LJ,..LI..---L~..........~.....
•1
-
SUSPENDED SEDIMENT CONCENTRATION
(mQ /lIter)
-
Figure IV-7.Empirical relationship of naturally occurring turbidity
versus suspended sedi~ent concentration for rivers in
Alaska,sampled during ~ay -October,1976-1983 (Lloyd
1985,derived from data provided by USGS).
IV-43
Table IV-8.Difference in compensation depths calculated from with-project suspended sediment
concentrations (mg/l)using two different relationships between turbidity (NTU)and TSS.
Forecast TSS Estimated Corresponding Compensation
Concentrations NTU Range Van Nieuwenhuyse
l.30 to 200 mg/l a)60 to 400 NTU 3.5 to 1 feet
b)10 to 40 NTU 4 feet
2.30 to 130 mg/l a)60 to 260 NTU 3.5 to 1 feet
b)10 to 30 NTU 4.5 feet
.......3.10 to 80 mg/l a)20 to 160 NTU 4 to 1.5 feet
<
I
.po b)5 to 15 NTU 5 feet.po
1.Peratrovich.Nottingham and Drage Inc.and Hutchinson 1982.
2.Stages I and II.Harza-Ebasco 1985a.
3.Stage III.Harza-Ebasco 1985a.
a)R&M Consultants 1984c.
b)Lloyd 1985.
J J "J ..~I J ,I J I 1 )I •B
r
j
Primary production in the middle reach of the Susitna River presently
appears to be 'concentrated in the spring and fall periods of loW
turbidities,although no quantitative data are available to document
thi s observati on.Constant,year-round turbi di ty 1eve 1sin the range
of 60 to 600 NTU would likely reduce the level of primary production
during these transition periods,although primary production may
increase during summer months.The net result of these opposing
processes has not been forecast at present.
IV-45
-------------Of
Instream Temperature and Ice Processes
Temperature Criteria for Fish
For the range of stream temperatures encountered in northern rivers,
increases in stream temperature generally cause an increase in the
rate of chemical reactions,primary production,and cycling of
allochthonous food sources.Fish,being poikilothermic inhabitants of
the river,adjust their body temperatures to match the temperature of
the water.As stream temperatures increase,rates of digestion,
circulation and respiration of fish increase.Thus,there is an
overall increase in the rate of energy input,nutrient cycling and
energy use by fish as any northern river system warms.
Each species of fish is physiologically adapted to survive within a
tolerance range of stream temperature.Within this tolerance range
there is a narrower range of "pre ferred"temperatures at which metabo-
lism and growth rates of individuals are most efficient.Outside the
tolerance range are upper and lower incipient lethal limits.
For the middle Susitna River,the preferred temperature range of adult
salmon is 6 to 12°C (Univ.of Alaska,AEIDC 1985a).Juvenile salmon
appear to prefer slightly warmer temperatures,generally ranging from
7 to 14°C (Table IV-g).These temperatures are consistent with the
preferred temperature range of 7 to 13°C reported by McNeil and Bailey
(1975)for Pacific salmon.The preferred temperature range for salmon
incubation is generally between 4 and 10°C.
The time required for the incubation of salmon embryos is directly
related to stream temperature.Development rates increase with rising
stream temperature up to approximately 14°C.Above this,further
temperature increases are considered detrimental.Salmon embryos are
also vulnerable to cold temperatures until they have accumulated
IV-46
"....
-
-
-
Table IV-9.Preliminary stream temperature criteria for Pacific salmon
developed from literature sources for application to the Susitna
River (University of Alaska,AEIDC 1984).
Temperature Range (OC)
Species Life Phase Tolerance Preferred
Chum Adult Migration 1.5-18.0 6.0-13.0
Spawning 1 1.0-14.0 6.0-13.0
f""'l Incubation 0-12.0 2.0-8.0
Rea ri ng 1.5-16.0 5.0-15.0
Smolt Migration 3.0-13.0 5.0-12.0
~,
Socke~fe Adult Migration 2.5-16.0 6.0-12.0
Spawning 1 4.0-14.0 6.0-12.0
Incubation 0-14.0 4.5-8.0
Rearing 2.0-16.0 7.0-14.0
Smolt Migration 4.0-18.0 5.0-12.0
P'i nk Adult Migration 5.0-18.0 7.0-13.0
Spawning 1 7.0-18.0 8.0-13.0
Incubation 0-13.0 4.0-10.0
Smelt Migration 4.0-13.0 5.0-12.0
Chinook Adult Migration 2.0-16.0 7.0-13.0
Spawn-j ng 5.0-14.0 7.0-12.0
Incubation 1 0-16.0 4.0-12.0
Rearing 2.0-16.0 7.0-14.0
Smolt Migration 4.0-16.0 7.0-14.0
I"""r
i Coho Adult Migration 2.0-18.0 6.0-11.0
Spawning 1 2.0-17.0 6.0-13.0
Incubation 0-14.0 4.0-10.0
Smelt Migration 2.0-16.0 6.0-12.0
1 Embryo incubation or development rate increases as temperature rises.
Accumulated temperature units or days to emergence should be determined for
each species for incubation.
IV-47
approximately 140 centigrade temperature units (CTU)I,after which
their sensitivity to cold temperatures has passed and the incubating
embryos can tolerate water temperatures near O°C for extended periods
of time.
Table IV-IO provides a comparison between the number of CTU that
resul ted in 50 percent hatching and 50 percent emergence of chum
salmon alevins under both field and laboratory environments.The
number of temperature units that resulted in 50 percent hatching and
50 percent emergence of chum and sockeye alevins at selected middle
Susitna River sloughs appear to be similar to that required by Alaskan
stocks of these species under controlled conditions (ADF&G,Su Hydro
1983c).Collectively,these data indicate that 400 to 500 CTU can be
used as an index for 50 percent hatching of chum and sockeye eggs.
The relationship between mean incubation temperature and development
rate for chum embryos is presented in the form of a nomograph
(Fig.IV-9).This nomograph can be used to estimate the date of 50
percent emergence given the spawning date and the mean daily intra-
gravel water temperature for the incubation period.A straight line
projected from the spawning date on the left axis through the mean
incubation temperature on the middle axis identifies the date of
emergence on the right axis.
Instream Temperature Processes
Stream temperature in northern rivers responds primarily to the
seasonal variation of the local climate and hydrologic conditions.
1A centigrade temperature unit (CTU)is the index used to measure the
influences of temperature on embryonic development and is defined as
one 24 hour period 1°C above freezing (GoC).Hence stream tempera-
tures at 4.7°C for 3 days would provide 14 centigrade temperature
units.
IV-48
~,
-
.....
~,
-
...
Table IV-10.Comparison of accumulated centigrade temperature units (CTU)
needed to produce 50 percent hatching of chum salmon eggs and 50
percent emergence of chum salmon alevins at selected sites on the
Susitna River with those required under controlled incubating
environments elsewhere in Alaska (from ADF&G,Su Hydro 1983c).
Brood CTU required CTU required 1
Locatlion Year for 50%Hatching for 50%Emergence
Susitna River -Slough 8A 1982 539 2
Susitna River -Slough 11 1982 501 232
~
Susitna River -Slough 21 Mouth 1982 534 283
Cl ear Hatchery 3 1977 420 313~
Clear Hatchery 3 1978 455 393
Eklutna Hatchery4 1981 802 209
USFWS Laboratory Anchorage 5 1982 306
~,5USFWSLaboratory-Anchorage 1982 448
USFWS Laboratory -Anchorage 5 1982 489
USFWS Laboratory -Anchorage 5 1982 472
1 Calculated from the time of 50 percent hatching to the time of 50 percent
emerogence.
2 No emergence had occurred as of April 20.
3 Raymond (1981).
4 Lore!n Waldron,Eklutna Hatchery,personal communication.
S Adapted from Waangard and Burger (1983).
IV-49
.'1!W,'Pl .,........"'!'"""'-----_
~
Emergence
T (C)Date
""'"
Spawning June 10
Date
1.0 ~
June I
-l5 May20
July 20 MaylO
2.0
Augl
May I
.2.5
AuglO April 20
3.0
Aug 20 3.5 April 10
4.0 1R'Jl¥i!>
April I
Sept I
4.5 //
./
/
Sept 10 /"5.0 March 20
5.5
Sept20 6.0 March fa
6.5
7.0 March I
Oct I ~
Oct JO
Feb 20
,-
FeblO
Febl .....
Jan 20
Jan 10
Jan I
Figure IV-9.Chum salmon spawning time versus mean incubation
temperature nomograph (Univ.of Alaska,AEIDC 1985a).
IV-50
-
Heat transfer between the atmosphere and an open water surface prin-
cipally occurs through convection,evaporation/condensation and
radiation.Heat transfer by convection and evaporation/condensation
responds directly to wind speed and the temperature differential
across the air-water interface.Radi ati ve heat transfer consi sts of
two types:shortwave and longwave radiation.Both short-and long-
wave radiation are significantly influenced by basin topography,
percent cl~ud cover,and surrounding vegetation.At higher latitudes
'incoming shortwave radiation is highly variable because of seasonal
differences in the solar azimuth which influences the intensity of the
shortwave radiatlon per unit area and the length of the dayl ight
period.
In addition to atmospheric processes,water temperature in the middle
Susitna River is influenced by its water sources.These are:glacial
melt,tributary inflow,and groundwater inflow.The relative
importance of each of these to mainstem flow and temperature at Gold
Creek varies seasonally.
Tributary inflow increases during snow melt periods and in response to
rainstorms,while the occurrence of glacial meltwater is predominantly
a summer phenomena.Groundwater inflow,however,appears to remain
fairly constant throughout the year.Hence its relative importance
'increases during winter as inflows from glacial melt and surface
Irunoff cease.Tributary inflows themselves diminish to base levels
maintained by groundwater inflow from their sub-basins.
The temperature of these i nfl uent sources also va ri es.Groundwater
Iremains near 3 to 4°C throughout the year (ADF&G,Su Hydro 1983c).
\~hile glacial meltwater at the headwaters of the Susitna River is near
(J°C,but it is warmed by the heat transfer processes described earlier
as it flows downstream.Temperature of tributary waters are generally
cooler than the temperature of the mainstem,especially during May and
.June when most of their streamflow consists of snow melt (Fig.IV-I0).
Tributary inflows characteristically hug the mainstem shoreline after
IV-51
______,,_~l\-"---w ------------------
15
14 ---Simulated Tributary Temperature
13 CJ Nean '81/'82 Temperature at
RM 150
12 ++Hean 181/'82 Temperature at
RM 110
11 -i 0 ++++
0 .~0 +0
10 Ci +0 ++u 0 0
'-"CJ 0 0
w 9 ~rx:
:;::J +E-<-.--:-----0--.
C'2 8 --0.,..-...
r.>1 /'-...
~....~G:1 7 /'.....
....~H ,.,
"
6 /........"-</,
I
m 5 /'...N /,,
I ,
4-i ,.,
3 -l I
I'fi',
!"
f2-+,
0 ,
"
1 --i '\
0 ,m
$'\O~JUNE I JULY I AUGUST I SEPTEMBER r OCTOBER
Figure IV-IO.Comparison between average weekly stream temperatures for the Susitna River and
its tributaries (adapted from Univ.of Alaska.AEIDC 1985a).
,J ,J l .,'.~.I ,J J ,t .~J J J j J
-
,....
!
.r-
I
f"">
I
converging with the Susitna River,forming a plume that may extend
several hundred feet downstream.Hence,tributary water temperatures
determine surface water temperatures in tributary mouth habitats but
have little effect on mainstem water temperatures.
In general,mainstem water temperatures normally range f~om zero
during the November-April period to 11 or 12°C from late June to
mid-July.Water temperatures typically increase from a to BOC during
l~ay and gradually decrease from 9 or IOoe in early September to O°C by
mid to late October.Water temperatures in side channels reflect
mainstem temperatures unless the mainstem discharge is too low for the
side channel to convey mainstem water.Surface water temperatures in
side sloughs,except when overtopped by mainstem flow,are independent
of mainstem water temperatures even though both may occasionally be
the same temperature (Table IV-II).
Sloughs receive nearly all of their clear water flow from local runoff
and groundwater inflow.When sloughs receive substantial inflow from
snowmelt or rainfall runoff~surface water temperatures will reflect
the temperature of that runoff.Due to relatively large surface areas
in comparison to flow rates,surface water temperatures in side
sloughs respond markedly to changes in solar radiation and air
temperature.Surface water temperatures typically reach 5 or 6°C in
quiescent areas within side sloughs by mid-April J approximately one
month before similar water temperatlJres are reached in mainstem and
side channel areas.Daily fluctuations in side slough surface water
temperatures are more exaggerated than for mainstem or side channel
vola ter temperatures (Estes and Vi ncent-Lang 19B4b).Duri ng wi nter,
slough flow is primarily maintained by upwelling groundwater which
possesses very stable temperatures around 3°C (ADF&G,Su Hydro 1983c).
Hence,surface water temperatures in side sloughs are significantly
influenced by the thermal quality of the upwellings;often remaining
well above DoC throughout most of the winter.
Side sloughs are occasionally overtopped by mainstem water when the
rnainstem ice cover is forming.The sudden influx of large volumes of
IV-53
Table IV-II.Comparison between measured surface water temperatures (DC)in side sloughs and simulated average
monthly mainstem temperatures (from ADF&G,Su Hydro I983b,I983c).
Note:Mainstem temperatures are simulated without an ice cover and warm earlier in the spring than what
naturally occurs.Thus the April mainstem temperatures are probably warmer than what would occur •
,I I J J .~i'J .1 J 1 •J 11 .i
-I
-
,...
-I
-
-
zero degree water during freezeup severely disrupts the normal
relationship between intragravel and surface water temperatures.Once
the slough is overtopped,the small volume of relatively warm slough
water,which serves to buffer submerged upwell ing areas from;extreme
cold,is immediately replaced by a large volume ofOoe water and slush
"ice.As a result,the warm influence of the upwelling groundwater is
diminished and intragravel water temperatures decrease from
approximately 3°e to near O°C (ADF&G,Su Hydro 1983c).
I~similar condition occurs during spring breakup if ice jams cause
large volumes of near-zero degree mainstem water to flow through side
sloughs,flushing them of their substantially warmer surface water.
Although little data are available for this period,intragravel water
temperatures are not suspected to be as adversely affected by over-
topping events during breakup as they are by overtopping during
freeze-up because of the shorter duration of the breakup events.
!~ith-Project Temperature Conditions
The cooling and warming of the middle Susitna River by the atmospheric
processes would not be altered by the proposed project.However,
construction and operation of the proposed Susitna Project would
redistribute the available water supply and its associated heat energy
through the year.During the summer months the reservoir would store
11eat while releasing smaller than natural flows hav'ing lower than
natural temperatures.For the remainder of the year,both the amount
and temperature of .the released water would be greater than natural.
Addition of Devil Canyon reservoir would amplify the deviation of
,,,,ith-project stream temperatures from naturally occurring summer and
,,,,inter temperatures at any given location within the middle Susitna
River.In effect,the addition of Devil Canyon Reservoir would result
in naturally occurring stream temperatures being affected further
downstream.Those porti ons of the Sus itna Ri ver most affected by
with-proj ect stream temperatures wi 11 be ma instem and side channe 1
IV-55
______ww'''''.._....,.__-----------_
\
areas upstream from the three ri vers confl uence (RM 99)(Uni v.of
Alaska,AEIDC 1985a).
Project design and operation will influence the temperature and flow
rate of water discharged from the dam(s).Table IV-12 displays the
s imul ated downstream temperatures for two summer situati ons:water
week 34 (May 20-26),where the downstream rel ease temperatures are
equal but release rates differ,and water week 45 (August 5-11)where
release rates are equal but their temperatures differ.The l.8°e
temperature difference shown in the second case results in a greater
difference .in downstream temperature than occurs by changing
streamflow 810 cfs,as shown in the first case.Table IV-13 displays
downstream temperatures for two wi nter cases:(I)where reservoi r
outflows are the same but flow volumes change (in this case a 59
percent increase)and (2)where dam release flows are relatively
constant (note:actually an 11 percent increase)but the temperatures
of the reservoir outflows differ by approximately 1°C.As indicated
by the previous example for summer releases,varying the temperature
of the reservoir outflow results in greater downstream temperature
differences than does varying the reservoir outflow.Hence,it can be
concluded that within the anticipated operating range of the project,
the temperature of the reservoi r outflow has a greater infl uence on
downstream water temperatures than flow rate.
However,basin climate is the most significant variable influencing
winter stream temperature and river ice conditions (APA 1984a).
Table IV-14 illustrates the substantial influence winter air
temperature has on downstream water temperatures.A decrease in air
temperature of approximately 8°C resulted in stream temperatures of
O.5°e to occur about 20 miles farther upstream.
Because of the possibility of using warm water releases from Watana
Reservoirs to control ice cover formation on the middle Susitna River,
Harza-Ebasco (l985c)evaluated alternative winter operating policies
and intake designs which might effect the temperature of reservoir
IV-56
-
-
.....
-
--
Table IV-12.Downstream temperatures COC)resulting from differences in summer
reservoir release flows and temperatures.
Water Week 34
(May 20 -26,1981)
Water Week 45
(August 5 -11,1974)
Dam Release:
10,950 cfs 10,950 cfs
Temp:
8.1°e 9.9°e
Middle
River Cross
Section River Mile
Dam Release:
6080 cfs
Temp:
3.9°C
2002
Demand
5270 cfs
2020
Demand
2002
Demand
2020
Demand
68 150 4.5 4.5 8.2 9.9
53 140 4.9 5.0 8.5 10.1
33 130 5.4 5.5 8.6 10.1
23 120 6.0 6.1 9.0 10.4
13 110 6.5 6.7 9.4 10.7
3 99 7.1 7.3 9.8 11.0
IV-57
........._---,-------------------------------------
Table IV-13.Downstream temperatures (OC)resulting from differences in winter
reservoir release flows and temperatures.
-
Water Week 9 Water Week 22
(Nov.26 -Dec.2 1970)(Feb.25 -March 3,1982)~
Dam Release:Dam Release:
7770 cfs 12,370 cfs 7190 cfs 8000 cfs ....Temp:Temp:
103°C 103°C 2.8°C 1.7°C
Middle
Ri ver Cross 2002 2020 2002 2020 ""'"
Section River Mile Demand Demand Demand Demand
68 150 1.3 1.3 2.7 1.7
53 140 0.7 0.9 2.2 1.2
33 130 0 0.4 1.5 0.7
23 120 a 0 0.8 0.1
13 110 a a 0.2 0
3 99 a 0 a 0 -
IV-58
-:Table IV-14.Comparison between simulated downstream water temperatures for
constant reservoir outflow conditions and different air
temperatures.
Water Week 8 Water Week 18
(Nov.19 -26,1981)(Jan.28-Feb.3,1983)
-Dam Release:Dam Release:
7,590 cfs.7,600 cfs
Middle River Release Temp:1.9°C Release Temp:1.9°C
R"iver Cross Mile Ai r Temp:(Talkeetna)Air Temp:(Talkeetna)
Sect'i on -11.6°C -3.4°C
68 150 1.8 1.9
53 140 1.3 1.6
33 130 0.6 1.2
23 120 0 .8
13 110 0 .5
3 99 0 0
Note:Both simulations are for Devil Canyon dam,2002 Demand.
IV-59
------,---------'----------------------------
outflows.The alternative policies evaluated include lIinflow
temperature matchi ng,II IIwarmest water avail ab 1ell and n lowest port.II
The inflow-matching policy,which was used for the ltInstream Ice
Simulation Studyn (Harza-Ebasco 1984c)and has been adopted'by the
Alaska Power Authority for the License Application studies (APA 1983,
1985),represents a year-round attempt to match the reservoir release
temperatures with the natural temperature of the flow enteri ng the
reservoir.Inflow temperature matching results in the release of the
coldest water available to the power intakes during winter.The
warmest water policy represents a year-round policy of releasing the
warmest water available to the power intakes.For both inflow-
matching and warmest water policies,the particular intake port
selected for operation will vary with the changing reservoir levels
and temperature profiles.The lowest port operating policy means that
the lowest port of the multi-level power intake will be operated
year-round regardless of water temperatures.
The wanllest water and lowest port operating policies tend to reduce
the maximum upstream extent of the ice cover as well as its thickness.
These reductions result in fewer sloughs being overtopped relative to
the inflow matching policy.However this trend does not hold for all
situations due to the influence of antecedent seasonal climatic
conditions.With the addition of Devil Canyon Dam (Stages II and III)
these alternative operating policies have no significant effect on ice
cover over the inflow matching policy.
Use of a low level intake port would also tend to reduce somewhat the
upstream extent and thickness of the ice cover.However,substantial
reducti ons in the ice conditi ons are not expected to occur
consistently unless a very low intake port is provided (Harza-Ebasco
1985d).
IV-60
-
-
Ice Processes
Figure IV-ll diagrams ice formation processes within the middle
Susitna River.In order to understand the flow chart and subsequent
discussions in this text,the following definitions for the most
common types of ice found in the middle Susitna River have been
adopted from R&M (1984b).
o Frazil·-Individual crystals of ice generally believed to
form around a nucleating agent when water becomes super-
cooled.
-
""'"'
o
o
o
a
Frazil slush -Frazil ice that agglomerates into loosely
packed clusters resembling slush.The slush eventually
gains sufficient mass and buoyancy to counteract the flow
turbulence and float on the water surface.
Snow sl ush -Simi]ar to frazil sl ush but formed by loosely
packed snow particles in the stream.
Black ice -Black ice initially forms as individual crystals
on the water surface ,in near-zero velocity areas in rivers
or underneath an existing ice cover.These crystals develop
in an orderly arrangement resulting in "a compact structure
which is far stronger than slush ice covers.Black ice
developing in the absence of frazil crystals is characteris-
tically translucent.This type of ice can also grow into
clear layers several feet thick within the Susitna slush ice
cover.
Shore ice or Border ice -This forms along flow margins as a
result of slush ice drifting into low velocity areas and
freezing against the channel bed.
IV-61
Backwaters and
.loughs
low veloetty areal
«I ft /sec)
SHORE ICE
Atmospheric
Coollog
Malnstem and
sid.cha nnels Snowfall
high velocity areas
(>1 1t /sec)
Upstream progression
of unconsolidated
Ice cover
iWithcompression
-
Figure IV-ll.Generalized flowchart of ice formation processes
within the middle reach of the Sus;tna River.
IV-52
-
.-
o
o
Freezeup
Ice bridges -These generally form when shore ice grows out
from the banks to such an extent that a local water surface
constriction results.Large volumes of slush ice may not be
able to negotiate this constriction at the same rate as the
water velocity.An accumulation of slush subsequently
occurs at the constriction,sometimes freezing into a
continuous solid ice cover or bridge.This ice bridge
usually prevents slush rafts from continuing downstream,
initiating an upstream accumulation or progression of ice.
Hummocked ice -This is the most common form of ice cover on
the Susitna mainstem and side channel areas.It is formed
by continuous accumulation of consolidated slush rafts that
progressively build up behind ice bridges,causing the ice
cover to migrate upstream during freezeup .
I"'"
i
-i
Frazil Ice Generation.Most river ice covers are formed as a result
of the formation and concentration of frazil ice.When river water
becomes sl ightly supercooled (GoC),frazil crystal s begin to form by
nucl eati on or by a mass exchange mechani sm between the water surface
Cind the cold air.In the Sus itna Ri ver fi ne suspended sed-iments may
be the nucleating agent in the Susitna River.In the mass exchange
mechanism,initial nucleation occurs in the air above the water
surface and the ice crystals fall into the water (Ashton 1978).
Frazil crystals initially form as small disk-shaped crystals only a
few millimeters in diameter.However,these small ice crystals grow
tapi dly in cold water and accumul ate as frazil slush masses,float
along on the stream surface.Snowfall often contributes to nucleation
ilnd accelerates frazil formation of floating snow slush.The slush
mass usually breaks up into individual slush floes within turbulent
portions of the river and continue drifting downriver until stopped by
'ice bridges at·river constrictions (Michel 1971;Ashton 1978;Oster-
kamp 1978).The accumulation of drifting slush masses against an ice
bridge results in the upstream progression of the river ice cover.
IV-63
--_._......_--_....
Frazil ice which contacts and attaches itself t the streambed is
called anchor ice.Frazil ice only attaches to the bed when it is in
the "ac tive"state.That is,when climate conditions are such that
the entire body of water at a given location is supercooled.Anchor
ice often accumulates fine sediment by filtering water flowing over
and through it.When air temperature rise or solar radiation
increases,the stream temperature will warm from a supercooled
condition to freezing.This results in a weakening of the bond
between the anchor ice and the streambed.Flow momentum and buoyancy
forces may become sufficient to discharge the anchor along with
attached fine sediment and gravels.The buoyant anchor floats
downstream to become included in the ice cover or to melt and release
its sediment load.
Genera 11y,frazil ice fi rst appears in the Sus itna Ri ver by
mid-September between the Denali Highway bridge and Vee Canyon.This
ice drifts downriver,often accumulating into loosely-bonded slush
floes,until it melts or exits the lower Susitna River into Cook
Inlet.Approximately 80 percent of the ice passing through the three
rivers confluence into the lower Susitna River during freezeup,is
produced in the upper and middle Susitna River,while the remaining 20
percent is produced in the Talkeetna and Chulitna Rivers (R&M I985b).
An excess of 50 percent of the ice occurring in the lower Susitna
River downstream from the Yentna River confluence is produced by the
Yentna River (APA 1984a).
Talkeetna to Gold Creek.The leading edge of the ice cover usually
arrives at the confluence of the Susitna and Chulitna Rivers (RM 99)
during November or early December (Table IV-15).The slush ice front
progression from the Susitna/Chulitna confluence generally terminates
in the vicinity of Gold Creek,about 35 to 40 miles upstream from the
confluence,by late December or early January.Water flowing under
the river ice cover often erodes the underside of the ice,causing
open leads in the river ice cover downstream of the ice front.This
usually occurs shortly after the initial stabilization of a slush ice
IV-64
ilMl"jI.,
-
""'"
-
-
Table IV-'15.Summary of freeze up observations for several locations within the Talkeetna to Devil Canyon
reach of the Susitna River (R&M Consultants 1981a,1982b,1983a,1984b).
Location River Mile 1980-1981 1981-1982 1982 -1983 1983~1984
Ice Bridgl~or Ice Front At
Susitna-Chulitna confluence Nov.29 Nov.18 Nov.5 Dec.8
Leadi ng Edge Near
Gold Creel<Dec.12 Dec.31 Dec.27 Jan.5
Approximate Freezing Dates at
Susitna Chulitna
Confl uencl~98.6 Mid-Nov.Nov.5 Dec.9
"103.3 Nov.8
"104.3 Dec.
u,106.2 Nov.9
"108.0 Dec.2
"'112.9 Dec.3
~Lane Creel<113.7 Nov.15
McKenzie Creek 116.7 Nov.18
"118.8 Dec.5
Curry 120.7 Nov.20 Dec.21
F'"Slough 8 124.5 Nov.20
"'126.5 Dec.8
fI 127.0 Mid-Dec.Nov.22
Slough 9 128.3 Nov.29
n 130.9 Dec.1 Jan.5
Slough 11 135.3 Dec.6
Gold Creek 136.6 Dec.12 Early Jan.Jan.14 Jan.15
Portage Creek 148.9 Dec.23
I"""
IV-65
..
cover.These 1eads may freeze over with the onset of very col d ai r
temperatures.Generally most leads are closed by early March.
As the ice front moves upriver its rate of progression generally
decreases.In 1982,the progression rate slowed from an average of
3.5 mil es per day near the confl uence to 0.05 mil es per day by the
time it reached Gold Creek (RM 136).This was attributed to the
increased river gradient near Gold Creek and to the reduction in
frazi1 ice input from the upper Susitna River because it had developed
a continuous ice cover.The upper Susitna River generally freezes
over by border ice growth and intermediate bridging before the
leading edge of the middle river ice cover reaches Gold Creek.
Local groundwater levels are often raised as the leading edge of the
ice cover approaches.As the ice cover forms on the river,mainstem
water surface elevations rise in response to the blockage of
streamflow by river ice.This process of raising the water level in
the mainstem upstream of the ice cover is called staging.Increased
water surface elevations are then propagated through permeable river
sediments into surrounding sloughs and side channels.
Many sloughs do not form a continuous ice cover or an ice cover which
persists all winter due to the relatively warm (1-3°e)temperature of
upwelling groundwater (Trihey 1982;ADF&G,Su Hydro 1983c).However,
ice does form along slough margins,restricting the open water area to
a narrow,open lead.Some portions of the sloughs that form black ice
covers during the fall and early winter later melt out because
mainstem staging increases upwelling rates and the associated thermal
influence of the groundwater.These leads often remain open through
the remainder of winter.
Generally,an ice cover has formed on the Susitna River at Devil
Canyon (RM 150)by the time the ice front reaches Gold Creek (RM 136)
in early January (R&M 1983a).Hence,the ice front is slow to advance
upstream of Gold Creek because of the lack of slush ice from above
IV-66
-
-
Devil Canyon.Also the higher mainstem velocities above Gold Creek,
caused by the steeper channel gradient,make it more difficult for the
ice cover to advance by accumulation of slush ice against its leading
edge.Hence that portion of the river between Gold Creek and Devil
Canyon forms its ice cover 1ater in the year and by a different
process than the sub reach below Gold Creek.
Throughout the freezeup period shore ice extends out into the river
continually incorporating slush ice,snow,and black ice into the
formation.Extensive shore ice formations constrict the open water
channel of the mainstem and frequently form ice bridges across the
river.In the open water arep's between the ice bridges,frazi1 ice
adheres to the channel bottom,forming anchor ice.Anchor ice often
Clccumul ates formi ng submerged obstructions (dams)on the stream bed,
increasing local water turbulence which then contributes to increased
frazil generation.Sl ight backwaters are sometimes induced by the
anchor ice obstructions which affect flow distribution between
channels and cause overflow onto the shore ice.Within these
backwater areas,slush ice may freeze into ice bridges because of
reduced surface velocity.
Little staging has been observed on the middle Susitna River between
Gold Creek and Devil Canyon.AC,cordingly,sloughs and side channels
'in this portion of the river are seldom overtopped during freezeup.
Open leads often exist in side sloughs during winter due to ground-
water inflow.Open leads also occur in the mainstem,but in
association with high velocity areas between ice bridges.As opposed
to the segment downstream of Gold Creek few leads reopen in this
segment after the formation of the initial ice cover.
J3reakup
The ice cover on the Susitna River presently disintegrates in the
spring by a progression beginning with a slow,gradual deterioration
and ending with a dramatic breakup drive accompanied by ice jams,
IV-67
-----,--_.._-.,--------------.......-----
flooding,and erosion (R&M 1983a).Although breakup always occurs
betwee~late April and mid-May,its duration depends on the intensity
of solar radiation,air temperatures,and precipitation.
A pre-breakup period usually occurs by early April as snowmelt begins.
Snowmelt begins first at the lower elevations near the Susitna River
mouth and slowly works northward up the river.By late April,snow
has usually disappeared on the river south of Talkeetna and the
snowmelt is proceeding into the reach above the SusitnajChulitna
confluence.Tributaries to the lower river have usually broken out in
their lower elevations,and open water exists at their confluences
with the Susitna River.Increased flows from the tributaries erode
the Susitna ice cover for considerable distances downstream from their
confl uences.
As water levels in the lower Susitna River begin to rise and fluctuate
with spring snowmelt and precipitation,overflow onto the ice often
occurs.Standing water which accumulates in depressions on the ice
cover reduces the albedo (reflectivity)of the ice surface,and open
leads quickly appear.In the steeper gradient middle Susitna River,
the rising water level erodes the under-side of the ice cover and
portions collapse into the river and drift downstream forming small
ice jams at the end of the open lead.In this way,open leads
continually become wider and longer unt"d the ice cover is weakened
and breaks up in a dramatic drive.
The disintegration of the ice cover into individual fragments,or
floes,and the drift of these floes downstream and out of the river is
called the "breakup driven.The natural spring breakup drive is
largely associated with rapid flow increases,due to precipitation and
snowmelt,which lift and fracture the ice surface.When the river
discharge becomes high enough to break and move the ice sheet,the
breakup drive begins.Its intensity is dependent upon meteorological
conditions during the pre-breakup period.
IV-58
-
-
-
-
-
...-
-
Generally,the final destruction of the ice cover occurs in early to
mid-May when a series of 'ice jams break in'succession,adding their
mass and momentum to the next jam downstream.This continues until
the river is swept clean of ice,except for stranded ice floes along
shore.Ice that has been pushed well up onto banks above the water
level may last for several weeks before melting.
~1ajor ice jams generally occur in shallow reaches with a narrow
confining thalweg channel along one bank,or at sharp river bends.
~1ajor jams are commonly found adjacent to side channels or sloughs,
and may have played a part in their formation by causing catastrophic
overflow and scouring at some time in the past.This is known to have
happened at Slough 11 in 1976,as reported by local residents in the
area,when a large ice jam flood transformed a small upland slough
into a major side slough.
Breakup ice jams commonly cause rapid,local stage increases that
continue.rising until either the jam releases or the adjacent sloughs
or side channels become flooded.While the jam holds,flow and large
amounts of ice are diverted into acljacent side channels or sloughs,
rapidly eroding away sections of riverbank and often pushing ice well
up into the trees.
Effects of With-Project Instream Temperatures on Susitna River Ice
Processes
The most important factors affecting freezeup of the Susitna River are
ali r and water temperature,i nstream hydrau.l i cs,and channel mor-
phology.The headwaters of the Susitna River are commonly subjected
to freezing air temperature by mid-September,and slush ice has been
observed in the Ta 1 keetna-to-Devi 1 Canyon reach as early as 1ate
September.Breakup is primari ly i nfl uenced by antecedent snowpack
conditions,air temperature and spring rainfall.Initial phases of
ice cover deteri ora ti on commonly begi n by mi d-April,with ice-out
generally completed by mid-May (R&M 1983a),
IV-69-_..........._...-.-----------_............-----------'---------------
Instream ice modeling studies indicate that operation of the Susitna
River Hydroelectric Project would have significant effects on
downstream ice processes due to project-induced changes to winter
streamflows and temperatures (Harza-Ebasco 1984c).Winter streamflows
would be several times greater than natural and stream temperatures
woul d increase from aoc to between o.SoC and 3°C dependi ng upon the
location downstream of the dam(s)(Univ.of Alaska,AEIDC 1985a).
With-Project Simulations,Freeze-up.The rate at which a river
produces frazil ice is dependent upon the heat transfer across the air
water interface.Therefore,the magnitude of below freezing air
temperatures and the amount of open-water surface area are important
considerations.The rate of frazil ice generation has been observed
to decrease as surface area of a river segment conveys greater
concentrations of floating slush ice.Therefore the ice discharge
from a long river segment may approach a II sa turation ll condition in a
relatively short distance dependent upon the air-water temperature
differential.This II sa turation ll condition has been observed to occur
naturally.The upper Susitna River often produces large volumes of
frazil ice and no substantial additional generation is visually
discernable below Devil Canyon (R&M 1983a).
Frazi1 ice generated in the Vee Canyon to Denali Highway river segment
normally drifts through the middle Susitna River and provides a
principal source of slush ice for ice cover formation on the lower
Susitna River.The volume of ice supplied by the middle Susitna River
during freeze-up has been estimated to be approximately 80%of the
total ice supply at the Chulitna-Susitna confluence.With
constructi on of Watana dam and reservoi r thi s frazil ice woul d be
trapped in the reservoir,unable to reach its normal destinations.
Additionally,there would be a completely ice-free zone downstream of
Watana Dam due to above O°C reservoir outflow.With the construction
of Devil Canyon Dam the location of the zero degree isotherm would be
extended downstream,further reducing the amount of surface area
within the middle Susitna River available for frazil ice production.
IV-70
-
.....
-
Downstream of the O°C isotherm frazil ice woul d be produced as a
function of air temperature and open water surface area.Therefore,
if the O°C isotherm is relatively close to the dam{s),large volumes
of ice can still be produced in the middle Susitna River,and the
effects of "trappingll the upper river ice supply and providing an ice-
free zone downstream of dams would delay,but not prevent,formation
of an ice cover on the lower Susitna River.
Arrival of the lower Susitna ice front at the confluence of the Yentna
River (RM 26)usually occurs in late October or early November.This
timing is not expected to be significantly altered by the project in
spite of the reduced frazil ice supply from the middle Susitna River.
Frazil ice contributions from the Yentna River and other major
tributaries (Talkeetna and Chulitna Rivers)would not be influenced by
the project and are considered adequate to maintain initial bridging
of the lower Susitna River near RM 10 (APA 1984a).Based on this
assumption,November 1 was used in the instream ice analysis
(Harza-Ebasco 1984b)as a representative date for the ice front to
pass above the Yentna River confluence.However,reduced frazil input
from the middle Susitna River,combined with higher winter streamflows
and temperatures would cause about a three-week delay (relative to
natural conditions)of the ice front progression upstream of the three
rivers confluence with Stage I operating.With stage II and III of
the project in operation,the ice front progression would be further
delayed from mid-December until late December or early January
(Fig.IV-12a).
The warm water temperatures released from the dams would not cool to
the freez i ng 1eve 1 for several mil es downstream of the dams.Except
for some shoreline border ice,ice would not form in this reach with
Stage I operating.The maximum upstream extent of the ice cover
during an average winter is expected to be in the vicinity of RM 139,
however,it could vary from RM 124 to R~l 142 depending upon winter
<:1 imate and project operation.The extent of the ice cover would be
t'educed to the vi cinity of RM 133 with Stage II operati ng and to
IV-71
0)Duration of Ice -Covered Period on Middle Susltna River
I Nov I Dec I Jan I Feb I Mar I Apr I May I
,.Natural \1
..Staoe I .1
Stage 1I )j"
Stac;J8 nr >t1-'
®
t-l
-<
I
'"-..J
N
Maximum Upstream Extent of Ice Cover on Middle Susitno River
River Mile River Mile
100 114 133 139 150
I I I I I
Natural
~I w
Stage I 139
I ~
Staoe II 133
I ~
Stage m 114,~
Figure IV-12.Duration of the ice-covered period and maximum upstream extent of ice cover on the
middle Susitna River under natural and with-project conditions (adapted from Harza-
Ebasco 1985d).
,J j .1 )J I )I 1 I
RM 114 under Stage III (Fig.IV-12b)).The ice front would reach its
maximum upstream position between January and late March for Stage I
and late January to early March for Stage III.The location of the
ice front would fluctuate considerably throughout winter depending on
prevailing air temperatures and project operation.
Under natural conditions,low streamflows occasionally cause secondary
ice bridges to form upstream of the Susitna/Chulitna in advance of the
main ice front.With the project in place,these low flow conditions
~~uld not occur and intermediate ice bridging is not expected to occur
in the middle Susitna River.Increased winter streamflows would also
cause water surface elevations of the mainstem to be significantly
higher than natural.In the ice covered portion of the middle
Susitna,winter staging is forecast between two and seven feet higher
than natural.Downstream from the ice front,a gr.eater number of
sloughs and side channels woul d be more frequently overtopped than
occurs naturally (Table IV-16).
Upstream from the ice front I s maximum progress ion,water sur:face
elevations would be higher than normal but freezeup staging would not
occur.Water levels in that reach would be 1 to 3 feet lower than
natural freezeup levels with Stage I operating and 1 to 5 feet lower
with Stage III operating.No sloughs are expected to be overtopped in
this reach by winter streamflows.However,the lower water levels in
thi s reach may reduce the naturally occurri ng rate of groundwater
upwelling in the sloughs.
Simulations generally have been made using an inflow-matching
temperature criterion for operation of the multi-level intakes at
Watana Dam.That is,power flows will be selected from levels which
provide outflow temperatures most nearly equal to inflow temperatures.
During winter,the inflow temperature is DOC,but the outflow
temperature is generally in the range of 1 to 3°C.Additional ice
cover simulations have been made by Harza-Ebasco using a warmest water
available and lowest intake port operating policies (Harza-Ebasco
IV-73
Table IV-16.Occurrences where with-project1 maximum river stages
are higher than natural conditions (Harza-Ebasco
Susitna Joint Venture 1984c).
"""
-
1
~
Watana Watana and 2
Slough or River Only 2 Devil Canyon
Side Channel Mile Operating Operati ng
Whiskers 101.5 6/6 6/6
Gash Creek 112.0 6/6 5/6
6A 112.3 6/6 5/6
8 114.1 6/6 6/6 ~
MSII 115.5 6/6 6/6
MSII 115.9 6/6 6/6
Curry 120.0 6/6 3/6
Moose 123.5 6/6 4/6
8A West 126.1 5/6 4/6
SA East 127.1 4/6 2/6
9 129.3 4/6 2/6
9 u/s 130.6 3/6 0/6
4th July 131.8 3/6 2/6
9A 133.7 3/6 1/6
10 u/s 134.3 4/6 1/6
11 dis 135.3 3/6 0/6
11 136.5 4/6 2/6
Notes:
IICase C'instream flow requirements and 'Iinflow-matching"reservoir
release temperatures are assumed for with-project simulations.
2 For example,4/6 means that 4 of the 6 with-project simulations
resulted in a higher maximum river stage than the natural
conditions for corresponding winters.
IV-74
1985c).Both of these alternative temperature policies are only
marginally effective for preventing ice cover formation on the middle
Susitna River.In addition,water qual ity effects such as increased
turbi di ty and reduced,di sso 1ved oxygen may be other factors to
consider with releases from very low levels.
~jith-Project Si mul ati ons,Breakup.The normal spri ng breakup drive
vlhich occurs on the middle Susitna River in early May is brought on by
streamflow increases that lift and fracture the ice cover.The higher
than natural water temperature released from the reservoirs during
vii nter woul d cause the upstream end of the ice cover to decay as soon
(IS air temperatures began to warm to near freezing.Additionally,the
reservoirs would retain spring runoff,yielding a stable or gradually
decl ining downstream flow regime that would favor II me ltout ll rather
than "break up "of the ice cover.Spring meltout in the Middle Susitna
River with Stage I operating would be completed by late April,about
two weeks earl ier than the natural breakup.With the addition of
Stages II and III,the meltout would be further advanced,occurring in
late to early March,respectively (refer Fig.IV-12a).
Effects of Ice Processes on Environmental Conditions
Ice processes in the middle Susitna River are important for
maintaining the character of side slough habitats.Besides reworking
substrates and flushing debris and beaver dams from the sloughs that
could otherwise be potential barriers to upstream migrants,ice
processes are also considered important for maintaining the
qroundwater upwelling in the side sloughs during winter months.The
alluvial deposits that form gravel bars and islands between the
mainstem and side sloughs appear to be highly permeable,making it
possible for water to infiltrate from the river into the sloughs.The
increased stage associated with a winter ice cover makes it possible
for approximately the same hydraulic head to exist between the
mainstem and an adjacent side slough during the ice-covered period of
the year as that which exists during summer.Water surface elevations
observed in association with the March 1982 ice cover appeared very
IV-75
similar to water surface elevations resulting from summer discharges
of 18,000 to 19,000 cfs (Trihey 1982).Thus,the increased stage
associated with an ice cover on the river may provide an important
driving mechanism for maintaining the upwelling in the side sloughs
throughout the winter.
However,ice processes also have negative effects on fish habitat in
side sloughs.During freeze-up,staging may cause zero degree
mainstem water to enter side sloughs and negate the thermal value of
the upwelling groundwater.Juvenile fish and incubating eggs exposed
to zero degree water for extended periods are likely to suffer a high
mortal ity.
Ice jams during breakup commonly cause rapid and pronounced increases
in the water surface elevations of the mainstem.The water continues
to rise until either the ice jam releases or the water can spill out
of the mainstem into adjacent side channels or sloughs.This may
cause sections of riverbank to be eroded.Ice scars have been observed
on trees in some areas as high as 15 feet above the stream bank.The
sediment transport associated with these events can raise or lower the
elevations of berms at the upstream end of sloughs and side channels.
Ice floes left stranded in channels and sloughs during breakup can
influence flow velocities and cause alteration of the local channel
geometry.
As a result of project construction and operation it is expected that
only a portion of the middle Susitna River will be ice covered and
that the naturally occurring breakup drive would be effectively
eliminated.This would substantially reduce the effects of breakup on
side slough and side channel habitats.VegetatiDn and beaver dams may
become better established,and streambed geometry should become more
stable.The higher stages forecast for the ice covered portion of the
middle Susitna would result in more frequent and longer duration
overtopping of side slough habitats than occurs naturally.Because of
the adverse effects of zero degree water on incubating embryos and
juvenile fish,the increase in ice stage is generally considered
undesirable.
IV-76
-
-
-
V.INFLUENCE OF STREAMFLOW AND INSTREAM HYDRAULICS
ON MIDDLE RIVER HABITATS
-Habitat Types and Transformation Categories
Habitat type referred to in this document are portions of the riverine
environment having visually distinguishable morphologic,hydrologic,
a:nd hydraul ic characteristics that are comparatively similar.Six
major aquatic habitat types were described in Sections II and III:
rnainstem,side channel,side slough,upland slough,tributary,and
tributary mouth.These habitat types are not defined by biological
criteria;rather,they are characterized by differences in hydraul ics
a.nd turbidity.-Thus,both high and low quality fish habitat may exist
\\rithin the same habitat type.
-
In our analysis of the influence of stre~mflow and instream hydraulics
on habitat,we must consider the relative amounts of each habitat type
available.To this end,the total surface area of each habitat type
in the middle Susitna River has been estimated for mainstem discharges
ranging from 5,100 to 23,000 cfs using digital measurements on 1 inch
~1,000 feet aerial photographs (Klinger-Kingsley 1985).The
r'esults show that surface areas of some habitat types,such as upland
sloughs and tributa ry mouths,exhibit 1 ittl e response to rna i nstem
discharge (Fig.V-I),often,their wetted surface areas respond more
to local runoff from summer precipitation than to variations in
mainstem discharge.
Comparatively large differences exist between responses of mainstem,
side channel,and side slough surface areas,to mainstem discharges.
At 5,100 cfs,the combined wetted surface areas of mainstem and side
channel habitat types is approximately 36 percent less than their
combi ned surface area at 23,000 cfs.Si de slough surface area peaks
at 7,400 cfs,approximately 175 percent greater than at 23,000 cfs.
t~s a result,the total surface area of all c1 earwater habitat types
V-I-_...._--_._--------------------------------------
5000 r------------------------------,
MAINSTEM
1000
100
50
>--=:UPLAND SLOUGH:
10 '----'----'_"'"'-------L._'----'----'_"'"'------'-_"'---'------'_--'-----'-_"'----'------''-----'----'------'
5 10 15 20
Mainstem Discharge at Gold Creek (xl 0-3 cfs)
Figure V-I.Surface area response to mainstem discharge in the
Talkeetna-to-Devil Canyon reach of the Susitna River
(Rf~101 to 149).
V-2
.,,-
i
-I
I!""
I
r
within the river corridor increases from 65 acres at 23,000 cfs to 145
alcres of the ri ver corri dor at 7,400 cfs.Thi s represents four
percent of the total wetted surface area at 7,400 cfs,as compared to
only one percent at 23,000 cfs (Klinger-Kingsley 1985).
tIt some locations,such as major side channels and tributary mouths,a
designated habitat type persists over a wide range of mainstem
discharge even though the wetted surface area and habitat quality at
the location may change significantly.In other locations,the type
of habi tat ava il ab 1e may change from one type to another in response
to mainstem discharge (Klinger and Trihey 1984).An example is the
transformation of some side channels which convey turbid water when
mainstem discharge is near 23,000 cfs to clearwater side sloughs at
lower mainstem flows.
To facilitate tracking habitat transformation the location of 172
specific areas were marked on aerial photography (Klinger-Kingsley
1985).Each specific area was classified by habitat type and its
Yietted surface area measured onaeri a 1 photography which had been
obtained at several mainstem discharges.From this,eleven habitat
transformation categories were used by Aaserude et al.(1985)to
describe the transformation of specific areas from one habitat type to
another as mainstem discharge decreases below 23,000 cfs (Table V-I).
Figure V-2 presents a flow chart of the possible habitat
transformati ons that may occur between rna i nstem di scha rges of 23,000
cfs and 9,000 cfs.
Habi tat transformati ons are referenced from a ma i nstem di scharge of
~~3,000 cfs because that discharge approximates a typical summer flow
the (50 percent exceedance flow)for the months of June,July and
August (APA 1983b).Analysis can be performed for any stream flow
lless than 23,000 cfs for which aerial photography exists.
Photomosaics of the middle Susitna River are available for mainstem
discharges of:23,000;18,000; 16,000;12,500;10,600;9,000;7,400
and 5,100 cfs (Klinger-Kingsley 1985).The influence of declining
V-3
.-........_---_......._----------------------------------
Table V-I.Description of habitat transformation categories (Aaserude
etal.1985)*
Category °-
Category 1 -
Category 2-
Category 3 -
Category 4 -
Category 5 -
Category 6 -
Category 7 -
Category 8 -
Category 9 -
Tributary mouth habitats that persist as tributary
mouth habitat at a lower flow..
Upland slough and side slough habitats that persist as
the same habitat type at a lower flow.
Side channel habitats that transform to side slough
habitat at a lower flow and possess upwelling which
appears to persist throughout winter.
Side channel habitats that transform to side slough
habitats at a lower fow but do not appear to possess
upwelling that persists throughout winter.
Side channel habitats that persist as side channel
habitats at a lower flow.
Indistinct mainstem or side channel areas that
transform into distinct side channels at a lower flow.
Indistinct mainstem or side channel habitats that
persist as indistinct areas at·a lower flow.
Indistinct mainstem or side channel areas that
transform to side slough habitats at a lower flow and
possess upwelling that appears to persist throughout
winter.
Indistinct mainstem or side channel habitats that
transform to side slough habitats at a lower flow but
do not appear to possess upwelling which persists
throughout winter.
Any water course that is wetted that dewaters or
consists of isolated pools without habitat value at a
lower flow.
-
Category 10 -Mainstem habitats that persist as mainstem habitat at
a lower flow.
*Habitats were based on a reference flow of 23,000 cfs.
/
V-4
-
~~l "}"-'}"J 1 -~l 1 "}1 ~-l
<:
I
en
WETTED AREA OF SITE
@ 23,000 CFS
I
CLEAR WATER TURBID WATER
@ 23,000 CFS @ 23,000 CFS
Side Sloughs Distinct Channel Indistinct Channel (Shoals)
Tributarv Mouths Upland Sloughs @ 23,000 CFS @ 23.000 CFS
0 1
Dewatered
@ 9,000 CfS
9 I
Clear Water Turbid Water Turbid Water Clear Water
@ 9,000 CFS @ 9.000 CfS @ 9.000 CfS @ 9,000 CfS
I I
I t I I
With Apparent Without Apparent Side Channel Mainstem Become Distinct Remain Indistinct With Apparent Without Apparent
Upwelling Upwelling (less than lOY.Side Channels @ 9,000 Upwelling Upwelling
01 Flow)@ 9,000
2 3 4 10 5 6 7 8
Figure V-2.Flow chart classifying trp.transformation of middle Susitna River a~uatic habitat
types between two flows (Habitat Transformation Categories 0.-10),
mainstem discharge levels on habitat transformation is quite apparent
when the number of specific areas within each habitat transformation
category is plotted for each of these photomosaics (Fig.V-3).As
mainstem discharge decreases)the number of side channel sites
(Category IV)decreases)whereas the number of side sloughs
(Category V)and dewatered areas (Category IX)increase.Although it
is possible to describe the general availability of fish habitat using
Figure V-3,changes in the quality of side channel and side slough
habitat are not obvious.Hence,a more detailed analysis using
microhabitat variables (e.g.,depth,velocity)substrate)etc.)is
necessary to assess the significance of these habitat transformations
in terms of the ability of the middle Susitna River to support fish.
V-6
-
-
-
~I
-
CATEGORY 1 SPECIFIC AREAS CATEGORY 2 SPECIFIC AREAS
NaUIER IT SPCCIflC "CAS
60 """BC'IT SPECIfiC ~or~s
IIl'UIlIl Allll SID!SLOIJCIlS
50
60
50
stDI OWllItLS 1'Q SID!:StJlIlCHS "In!"I!<Tn tm/nL1J1<:
40 40
510074001600012500106009000
MAINST£M OIS(HARG[(efs]
180005100\740012500106009000
MAINSHH rHSCHA~G[(cf,)
o L-""'a----l;LUL-.....u-"L_..J.UA----l;t..(.lJL-.....u-"L_~:..a_..J
18000 16000
30
20
10
CATEGORY 3 SPECIFIC AREAS CATEGORY 4 SPECIFIC AREAS
.......,.IT SP{Clf IC ..rAS
60 60
"UMBER (E.SPECJF IC "CAS
SID!0WllIEI.S 1'Q SlIl!SLOllClIS IIITHOUT vtlrTn lIt'IIf:tLIIIC
50
40
30
20
50
40
3D
20
10
o
18000 16000 12500 10600 9000 ]q00 5100
>lAIHS1[M flIS(IlARf,!lefsJ HAlI/SHH OIS(HARG[lefs)
CATEGORY 5 SPECIFIC AREAS CATEGORY 6 SPECIFIC AREAS
"UMB!'Of SP(C Inc ...rAS
60 60
Ill11(STINCT SID!OWllIns 1'Q DISTIlIcr StDl ClWftlILS L"fDISTINcT HAINSTEIf ...,m 5101 ClWftl!I.A.ltU,S
50 50
40 40
20
30
5UJO7400900018000160001250010600
30
20
10
5100740090001800016000 12500 10600
o
MAINSHI'DISCHARGE lefs)MAINSl[M OISCHARGE lefs)
Figure V-3.Number of specific areas classified in each habitat category
for various Gold Creek mainstem discharges.
V-7
,_............==-~~'---_r ..·.........----------------.....-rr-----------------------------
CATEGORY 7 SPECIFIC AREAS
.,..,8(R OF S!'[tlflt AR[AS
60 'r------.:.~~=--------------___,
CATEGORY 8 SPECIFIC AREAS
HUMBeR or S!'{CIFlt AREAS
60 ,..;,---------------------
llllltsn~cr SIIlE OW<l<ELS TO SID£SLDUCIIS I11TK IIIKt"ll UI'II£l.LIllG
50
40
30
20
10
50
40
30
20
10
IlIIlISTl~CT StD.ClIAIlNELS TO SID'Sl.OOC>lS IIITKCIIJ'T IIIIITLl
lJ1"Wl.L.L!.~C
o
18000 16000
(ds I
o
18000 16000 12500 10600 9000
MA1NSTEM OISCHARGE (e,,)
7400 510n
CATEGORY 9 SPECIFIC AREAS
HUMB[R OF SP£CIFlC AR[AS
60 ;:::.::.:::...:::....:::..:=..:~::.:.:....-_----------1
SPECIllC JonAS TIlA1"llE\IATDl
50
40
CATEGORY 10 SPECIFIC AREAS
HUMalR or SP[CIFIC AREAS
60',-----------------------,
50
40
3030
20
10
oL-J:.:.iJ_J..:.:.L---.t:.:~--J~-~r.l...-~~~,:"=:"-J
18000 16000 12500 10600
MAIHSHM OISCHARGE (cf,]
Figure V-3 (Continued).
V-8
20
10
o
18000 16000 12500 10600 9000
MAINST[M 01SCHARGE {cf,I
7400 5100
-
-
-
-
-
~
I
-
Microhabitat Response to Instream Hydraulics
The response of depth and velocity of flow to variations in
streamflow.In part,the availability and quality of fish habitat is
affected by the effect of streamflow variations on the availability
and quality of spawning and rearing habitat has been modeled at
several side slough and side channel study sites (Estes and
Vincent-Lang 1984d;Schmidt et al.1984).Computer software used for
the model was developed by the USFWS Instream Flow and Aquatic Systems
Group (Bovee and Milhous 1978;Bovee 1982;Milhous et al.1984).
Spatial distribution of depths and velocities within a study site were
simulated at several different site-specific flows using the IFG-4 and
IFG-2 hydraulic models.The simulated depths and velocities were then
used in combination with numeric descriptors for other microhabitat
variables (upwelling,cover,and substrate)to describe physical
habitat at the study site as a function of streamflow.Thus,
integrated numeric descriptions of upwelling,depth,velocity,
substrate,and cover at each study site were obtained at various
flows.These descriptions were then weighed according to their
suitability for fish.Because of their sensitivity,spawning and
rearing salmon were chosen as indicator species and life stages (refer
to Section III).An index of habitat availability called Weighted
Usable Area (WUA)was calculated for both spawning and rearing.
Because all of the microhabitat variables respond,either directly or
indirectly,to streamflow variations,weighted usable area can be
considered a streamflow-dependent habitat availability index.The
macrohabitat responses of the evaluation species and life stages are
described below.
Spawning Salmon
Microhabitat Preferences.Generally,the influence of streamflow
variations on spawning habitat is evaluated using three microhabitat
variables:depth,velocity,and streambed composition (substrate)
V-9
,--_.__.......-----------........---.......--........._-------------------
(Wesche and Rechard 1980;Bovee 1982).However,a fourth variable,
upwelling,is also considered important for successful chum and
sockeye salmon spawning in the middle Susitna River (Estes and
Vincent-Lang 1984d).Upwelling has also been identified as an
important habitat component for spawning chum salmon at other
locations in Alaska (Kogl 1965;Koski 1975;Hale 1981;Wilson et al.
1981).
Of the four microhabitat variables used in the modeling processes,
upwelling is probably the most important variable influencing the
selection of redd sites by spawning chum and sockeye salmon.Spawning
is commonly observed at upwelling sites in side sloughs and side
channels possessing relatively broad ranges of depths,velocities,and
substrate sizes.However,portions of these same habitats possessing
similar depths,velocities,and substrate sizes,but lacking
upwelling,are not used by spawning chum or sockeye salmon (Estes and
Vincent-Lang 1984d).Because of this strong preference for upwelling
evident in field observations,a binary criterion was used for this
microhabitat variable.The habitat suitability criterion for
upwelling assumes optimal suitability for areas with upwelling and
non-suitability for areas without upwelling.
Streambed material size generally has an influence on the qual ity of
spawning habitat.The habitat suitability criteria developed by ADF&G
for chum and sockeye salmon spawning in side slough and side channel
habitats indicate that streambed materials one to five inches in
diameter provide optimal spawning substrates (Fig.V-4a).This size
range includes notably larger particles than the 1/4-to-3 inch size
range commonly cited in the 1 iterature (Hale 1981)as being most
suitable for spawning chum and sockeye salmon.The discrepancy
between the ADF&G and literature criteria may,in part,be
attributable to sampling procedures.However,it probably reflects
the dominant influence upwelling has on the selection of redd sites.
Apparently,such a small amount of good quality spawning substrate
exists in middle Susitna River habitats that both chum and sockeye
salmon use whatever streambed material sizes are associated with the
upwellings.
V-10
-
-
-
_.
-
-
-
1.0
.~
.6
X
lJJ .7
az .6A.>-
l-.5
-l
CD .4«
l-
:::l .3
(f)
.2
.1
0
1 2 :3 4
SI SA
5 6 7 6 9 10 II 12 13
SG LG RU CO BO
SUBSTRATE CODE
SUITABILITY CRITERIA
SOClCEYE CHUM
SUIISTRATE PARTICLE SUITABILITY SUlTA81L1TY
COOE --!!.3.L IN'OEX INOEX
I SI SILT 0.000 0.000
2 0.000 0.000
3 SA SAHO 0.000 0.025
4 O.fOO O.O~O
5 sc V8.,.0.500 0.200
G 0.'50 O.GOO
7 LG ,.,.1.000 1.000
8 1.000 1.000
'3 .~U 1 ...5"1.000 1.000
10 0.900 O.BSO
II CO 'e '0"0.250 0.700
I.0.100 0.250
13 80 :>'0·0.000 0.000
~SOCKEYE 111 CHUM
1.0
1.0O.z
0.0
••CHUM
~
0.0
1.3
ae
4.5
CHUM
SUITABILITY CRITERIA
SUITA81LITY
IHOEX
l.0
.9 \
\
\SOCKEYE
.8 \SUITA81l1TY CRITERIA
SUITABILITY
X \VE,1.:OCTTY H.lOEX
W .7 \0.0 1.0az\1.0 1.0B..6 2.0 O.~
>-\.'.0 0./
I-.5 ~4.5 0.0
-l \0---0 SOCKEYEa:l .4 \«I-\
:::l .3 \(f)'l.2 \
•1 b......
0
0 l.0 2.0 3.0 4.0 5.0
VELOCITY (FT/SEC)
~
I
t ,i
l ;
1.0 /
.9 9
I SOCKEYE CHUM.8 ,
SUITABILITY CRiTERIA SU1TA61LITY CRITERIA
X .7 I S1JITASU..:IT'l'SUIT.ABlUTYWr..Q!.E!!:!...lNOEX ~(NQE:XaI0.0Z0.00 0.00 0.0.6 )o.zo 0.0 0.20 0.0c.>-r 0.30 0.2 0.50 0.2
!::.5 0.50 0.9 O.BO 1.0
-l I 0.75 1.0 B.OO 1.0
a:l .4 I 8.00 1.0
«J
l-I 0---0 SOCKEYE -CHUM
.3:::l ~(f).
.2
Y.1
0
0 l.0 2.0 3.0 ':.0 5.0 6.0 7.0 8.0
DEPTH (FT)
I '!
,..,
I
Figure V-4.Habitat suitability criteria for slough spawning chum
and sockeye salmon (Estes and Vincent-Lang 1984d).
V-ll
Stream velocity is often considered one of the most important
microhabitat variables affecting spawning salmon (Thompson 1974;
Giger 1973;Wilson et al.1981).The habitat suitability criteria
developed by ADF&G for both spawning chum and sockeye salmon assigns
optimal suitabil ities to mean column velocities less than 1.3 fps
(Fig.V-4b).As the velocity at the spawning site increases above 1.0
fps,suitabil ity decl i nes more rapi dly for sockeye than for chum.
Microhabitat areas with mean column velocities exceeding 4.5 fps are
considered unusable by both species.
The ADF&G criteria assign slightly lower suitabilities to velocities
between 2 and 3 fps than criteria available in the literature (Bovee
1978;Estes et al.1980;Hale 1981;Wilson et a1.1981).This dis-
crepancy may exist because most data used to develop velocity suit-
ability criteria for spawning chum and sockeye salmon in the middle
Susitna River were collected in side slough habitats that typically
have a narrow range of low velocities.
Chum spawning data from streams and rivers in Washington state
indicate that higher velocities are frequently associated with chum
salmon spawning in mainstems than in side sloughs (Johnson et al.
1971;Crumley and Stober 1984).Table V-2 summarizes velocity data
collected at mainstem,tributary,and side slough locations of several
rivers of moderate size.Velocities measured over redds in Nooksack,
Illabot (Skagit),Skykomish,and Satsop sloughs averaged sl ightly
lower than spawning velocities determined for other habitat types.
We conducted sensitivity analyses in which WUA indices for spawning
chum salmon were calculated using both the ADF&G velocity criteria and
modified velocity criteria identical to the ADF&G velocity suitability
curve (Fig.V-4b)except that the optimal range of velocities for the
modified velocity criteria was extended from 1.3 to 1.8 fps.
Comparisons between the two WUA forecasts indicated an insignificant
V-12
-
-
-
Table V-2.Mean column velocity measurements (fps)collected at
chum salmon redds in several rivers of Washington state
(Johnson et al.1971).
-
Number of Velocity Mean-River Measurements Range Velocity
Nooksack Ri ver
Nooksack Slough 24 0.21-1.34 0.61
Maple Creek 20 1.22-4.11 2.52
Kenda 11 Creek 21 0.31-3.76 2.30
Skagit River
Main River 40 0.67-3.86 1.82-I1labot Creek 17 0.31-2.78 1.56
I11abot Slough 25 0.58-2.93 1.20
Dan Creek 50 0.52-3.09 1.81
Skykomish River
Skykomish Slough 31 0.41-2.22 1.31
Chico Creek 50 0.16-3.97 1.95
Kennedy Creek 50 0.47-3.16 1.60
Twanoh Creek 25 0.31-2.83 1.25
Jorsted Creek 50 0.60-3.16 1.68
Satsop River
Main River 50 0.14-2.33 1.25
Satsop Slough 50 0.00-2.27 0.56
Satsop Springs 30 0.12-1.70 1.22
~
r
V-13
-_........._--_.......-...._--------------------------------
difference (..::.5%)at low-to-moderate mainstem discharges.Even at
high mainstem discharges,where the modified velocity criteria with
its higher optimum might be expected to be significant,WUA forecasts
associated with the modified criteria did not exceed the forecasts
obtained using ADF&G velocity criteria by more than 10 percent.
These results do not appear to justify modifying the ADF&G velocity
suitability curve to include optimal velocities in excess of 1.3 fps.
Therefore,the velocity suitability criteria developed by ADF&G for
chum spawning will be used for the IFR analyses of side channel and
mainstem chum spawning potential.
The ADF&G habitat suitability criteria also indicate that depths in
excess of 0.8 feet are most suitable for spawning chum and sockeye
salmon (Fig.V-4c).This depth is slightly more conservative but
consistent with the 0.6 foot depths used elsewhere (Thompson 1972;
Smith 1973).Microhabitat areas with depths less than 0.8 feet
provi de subopt ima 1 spawni ng and depths of 0.2 feet or 1ess are un-
usable.These minimum depth criteria are consistent with values
presented by others as mi nimum·depth requi rements for spawni ng chum
salmon (Kog1 1965;Wilson et ale 1981).The suitability criteria
developed by ADF&G for depth are consi stent wi th criteri a used by
others and will be used in the IFR analyses.
Habitat Availability.WUA indices (habitat response curves)for
spawning chum and sockeye salmon at three side slough and four side
channel locations were developed by ADF&G using the variables and
suitability criteria discussed above.Both chum and sockeye salmon
have been observed spawning within,or in the immediate vicinity of,
four of these seven study sites (Barrett et a1.1984;Estes and
Vi ncent-Lang 1984d).Although minor differences exi st between the
habitat response curves for spawning chum and sockeye salmon at each
of these four study sites,the curves for the two species are similar
(Fig.V-5).The minor differences that exist between the curves are
V-14
-
-
.....
......
~I
-
--1 1 J 1 1 )
2&I 5LOUCH IIA
I2'"i
SIDE CI1ANNEl 'J,I
26 "~-----------";"'---------------""1
2~
606040
0
20
ow (cr5)
0
SIT I:rL +50(;l«YI:0 CHUM
<
SLOUCH 21
I
l-'
en
26
24
22
20
f ~~l~~51.....
ifw1
!j::'10 I~
·f ___~:I
III
:j
I ii
400
i J
300
i i
200
o .
100
SIT('LOW (~~~)KI:YI:
0
,:HV},I +'"
0.2o
8
6
...---.--~4-l~.~~
I .....~~~a---<)'-r--.---,-..,-~'~~--J--'-~I I.,;1.6..L-~-'ir--'I-'---:-'-"0.6 ,1.2
o I 0 .•'0.6 tThou.onrctS)
511"(fL~'"SOCKEYEoCHUM
14
16
12
22
20
IS
'0
f
a"'~;i~~"1.2Ll~
<~
"-~
LOwER 5JDL C~~!-H·a:'..I'
26
201 -
22 •
20
t 16
0 16"'.......-n~g 14
'g 12..,2
Ll~10.<~
"-'":I 8'"6
~
2
o·
0 0"0.8 1.2 1.6 2 2.<
sl/~h?~o:nrc}.S)
0 CI'IUM +SOCKEYE
18
8
,e
, 2
n
20
10
,4
f
ft...
;;~~~~l
~
Figure V-5.Compari son of ~'UA responses to site f1 o\'!for spavlni ng chum and sockeye
salmon at four middle Susitne River study sites (adapted from Estes and
Vincent-Lanq 1984d).
attributable to differences between depth and velocity suitabil ity
criteria.A slightly higher suitability is assigned to depths between
0.2 and 0.8 feet for sockeye,whereas a slightly higher suitability is
assigned to ve10cities in excess of 1 fps for chum salmon.
Except for a few isolated observations,all sockeye salmon spawning in
the middle Susitna River oc~urs in side sloughs that are also utilized
by chum salmon.The timing and spawning habitat requirements of
sockeye salmon are similar to chum salmon (Estes and Vincent-Lang
1984d),and chum salmon are both more numerous and widespread than
sockeye in middle Susitna River spawning habitats.Because of this,
and because of the similarities between habitat response curves,the
IFR analysis will focus on the response of chum salmon spawning
habitats and will use those WUA indices to estimate the response of
sockeye salmon spawning habitats.
Total wetted surface area and weighted usable area for spawning chum
salmon at six study sites are presented in Figure V-6.These sites
a re grouped into three di sti nct habitat categori es based on channel
morphology and hydraulics.In comparison to total surface area,low
WUA indices are forecast at all sites.By arbitrarily increasing the
total surface area of groundwater upwelling at Side Slough 21 to 15
percent and at Upper Side Channel 11 to 50 percent,WUA forecasts
increased at both sites without a notable change occurring in the
shape of the habitat response curve for either site (Fig.V-7).This
demonstrates that the maximum amount of spawning habitat potentially
available is determined by the total surface area of the upwelling.
The habitat response curve at Slough 21 peaks when the mainstem
discharge is approximately 28,500 cfs,while that for Upper Side
Channel 11 peaks near 23,000 cfs (Fig.V-8).At these discharge
levels,the alluvial berm at the upstream end of each site is
overtopped and the site-specific flows are approximately 70 cfs in
Slough 21 and 150 cfs in Upper Side Channel 11 (Estes and Vincent-Lang
1984d).Whenever the mainstem discharge is insufficient to overtop
V-16
-
-
.....
8.-0--00--....-00......:>-.....-......0:>----0<>-
I~:J
4.)
71'
E'e,oa
~iS~~.,
lB...l "'0"eo~'"JOD.,
20
10
"........-.
0
0 20
SLOUCH 8A
CHULt $.l.U.IGN SFiAWH.aNC
..0
sue,rLOYI (aS}
GO 80
100
10..
eo
t 70
<3
~50 r6.40~B
~l "0
l:!:J JO'"
"0
10
0
0 '00
SLOUGH 21
CHUlA SAUlO'"SPA_
200 JOO
SITe:n.ow (el'S)
240200co.2-0 USO
S'1&n..0Wli'(CTSl
UPPER SIDE CHANNEL 11
CJoiUfioI SAL.,L.40N SPAWN4NC
'20
110
100
10
t 80
0e-;;-70~!~~GO."'"so~:.
II:"0:J
'"'0
20
10
0
0500<1-00
SITE n.ow (C~)
SLOUGH 9
CJotuu.SA..l.)r.COH SPAWNtNC
200o
.40
1"'0
lJO
120
E 110
.00aeo;:-.0
~§00
~;1'0",j!
~.c ~~tJ
12 :iO:J
'"4,0
:~o
:lO
'0 di"""'m •••0
0
~,
I.-
SIDE CHANNEL 21
CHUW:SAUoION SPAWNiNC
250
2"'0
220
200
E''80
a ISOe:o-
is],...
~~'20...~
u~100<~...
'":J 80'"_0...
20
0
0 0.2 .0."
o WUA (STO-CO"'SINEOI iCROSSSURf'AC'E:AAEA.
1...2.1.6
(Tto.INndaJ
S~TE FLOW ~CFSI
O.e
a 8 II B B,e B
LOWER SlOE CHANNEL ·n
CHUM SA,L"MQH SPAWNING
0."
.3:z.~,
30r::!
.2arO
.26,0
....0
t "2'0.,"0'0~~!le.O
~~,eo
...j!...0
u~~'''0
'"100:J
'"eG
50
"0
20
0
0
-,
Figure V-5.Total surface area and WUA index for spawning chum salmon
at Habitat Category I,II,and III study sites (adapted
from Estes and Vincent-Lang 1984d).
\"""
i
V-I?
---....-'--....---~-----------------------f"i--------------------------------
LEGEND
Increased Upwelling
---AOF8G WUA
4003M300200I~O100
15 PERCE.NT INCREASE IN UPWELLING SURFACE AREA
00
_._--.....
';;-..........~-------r _~-------_."
SLOUGH 212.2.000
2.0.000
18,000
16,000
14,000
I,,<XX)
10,000
epeo
epOO
4IXYJ
2POO
0-1 I I I I I I I I
o
<II(
;:)•
-.......-
81 TE FLOW (CFS)
<
I
f-'co
2~022~20011~J!501201007~
50 PERC·ENT INCREASE IN UPWELLING SURFtrCE AREA
002~
~-~~-~------~~----~~.--,---
/
/
y/
UPPER SIDE CHANNEL II
C 10,000;:)
:.8,000
61XXJ
4,000
2,000
O~I I Io I I I iii i
-.......-
SITE FLOW (C FS )
Figure V-7.Simulated influence of increased upwelling on WUA for
spawning chum salmon at Slough 21 and Upper Side Channel 11.
J J J :,.J J t J J t •.1 J I
SLOUGH 21
28 CHU~SAL~ON SPAWNING
24
22
20
f 18
0 161Il~~"~-g 14~~12",0~e.10'"'":J IS'"8 -------------
4
2
a
a lQ 20 30MAJNSTdJt'~~~~aE(CPS)
UPPER SIDE CHANNEL 1 1
26 CHUM SA!..""ION Si=lAWN1NCi
24
22
2Q
..."1010~
"~;,..~~-c::.-r,
12 j~~r:!'-~"
-<-10 I
I"'''"...
CI:
:J e'"e
/"'4 ----./"2
a
40 0 10 20 30 ~;J~(~t.rSTEtTh8Is~~~d!:(C:="S)
SIDE CHANNEL 21
CHU~.5.A.l.MON SPAWNING25
24
22
20
t "1015.e";;,,
;:s~14
~~
"1
",,g
u'"'a<-...
CI:
:J 8III
B
41 ~:j
40 0 10 2Q 30 40MAIN~TEcrM~ISCa~O;6t;(crs)
c WUA (STO-COMSINEO)
SlOE CHANNEL 21
C.HUM SAlMQN SPAWNING
/
_./
10 20 30
MAINSTe:Uh~~~~ntR6E (CF"S)
SLOUGH 21
CHUM SAL~aN SPAWNING
'A 2Q JOU.:.JNSTe:gh8ISC~6E (CFS)
------------~
o 10 20 30
MA'NsrEahO'SC~R~~.CCFS)
WUA (STC-COM81~'.j~D)GRaSS SURFACE AREA
UPPER SIDE CHANNEL 11
CHUM 'SALMON SPAWNING'..0.-,----------------.....,....__---,
'00
gO
M
t 70 -1
0
BO l"'~~.;:s"g
~~~o 1"'~U'"
40 1<~...
'":J JO111
20 J
10
a
a
-
;~60
~!40I"""
:!20
:lQO
t '180
0 '1501Il~-"~-g '140"'~"','120"'~~t 100...
'":J 80111
BO
40
20
a
0
....,
-
Figure V-So Surface area and WUA response to mainstem discharge at
Habitat Category I,II,and III spawning sites (adapted
from Estes and Vincent-Lang 1984a).
!"""
I
V-19
_____ili\i~~,,_·fN------------------------~~-------_
their upstream berms,base flow at both sites is less than 5 cfs
(Estes and Vincent-Lang 1984d).The depth of flow at upwelling areas
is typically less than 0.5 feet at base flow,but increases to
1.a foot or more when the upstream berms are overtopped ~Fi g.V-9).
Velocities respond similarly to overtopping,typically increasing from
the a to 0.5 fps range to approximately 1.5 fps (Fig.V-10).
Depths and vel ociti es associ ated with baseflow and overtopped con-
ditions were compared to habitat suitabil ity criteria for spawning
chum salmon (refer Fig.V-4).The comparison indicates that the rapid
increase in WUA indices following overtopping (refer Fig.V-8)is
attributable to an increase of depth over upwelling areas.The
gradual decrease in WUA indices at higher site flows is due to mean
column velocities over upwelling areas exceeding the 1.3 fps optimum.
It is important to recognize the degree to which shallow depth
restrict both the availability and the quality of side slough spawning
habitat under nonbreached conditions.
Figure V-ll presents streamflow and habitat duration curves at four
study sites whi ch overtop at different rna i nstem di scharges.Each
habitat duration curve was constructed using daily WUA values derived
from average daily site flows.Daily site flows were determined using
the mainstem flow at Gold Creek and the site flow versus mainstem
discharge regression equations presented by ADF&G (Estes and
Vi ncent-Lang 1984d)for breached condit;ons.For nonbreached
conditions average daily site flows were estimated at 3 cfs on the
basis of Held experience and a limited number of flow measurements
reported by ADF&G (Estes and Vincent-Lang 1984d).
These duration curves accent the influence of the upstream berm
elevation (breaching flow)on site-specific streamflow and habitat
conditions.Category I sites which require the highest mainstem
di scha rges for overtoppi ng possess the most pers i stent WUA i ndi ces
duri ng the spawni ng season.Category II sites whi ch overtop when
mainstem discharge is between 10,000 to 20,000 cfs show distinct
V-20
-
-
-
-
j ,········1 ..,),·········1 -······'<~1 '~1 J )····1 -)1
20i FLOW =50 CFS
3.53.02.52.01.51.00.5
'~~
o
I
o
>-oz
~J0i-SUBOPTIMAL.OPTI MAL RANGE ,..-f
lIJa:u..
DEPTH OISTRI BUTION (ft.)
-<
I
N
>->
20 FLOW.5 CFS
3.53.02.52.01.5
OPT'MA L RAN GE
1.00.5
01 Fi)':;1 "Vil tll 1\1 1\,,I~~"I:::';';
°
.",41 1 1 i."f::::J~fr::;JJ:.'ii,',_ii'f i 'ii'1
~b.~UBOPTIMA,
I&J
::.10o
l&.In::
IL
DEPTH DISTRIBUTION (ft'>
Figure V-g.Frequency distribution of cell depth over upwelling areas in Upper Side Channel 11 at
site flows of 5 and 50 cfs.
I~OPTIMAL RANGE ..,....SUBOPTIMAL ...1
10
>-o
Z
lU
::;)8a
lUa::
LL.
FLOW·50 CFS
0.0 0.1 0.2 0.3 0.4 O.!S 0.6 0.1 0.8 0.9 1.0 1.1 1.2 1.3 1.4 U5 1.6 1.1 1.8
VELOCITY DISTRI BUTION (CFS)
I....OPTIMAL RANGE ....,~SUBOPTIMAL ..I
o
•I I I I I
0.0 0.1 0.2 0.3 0.4 O.!S 0.6 0.1 0.8 0.9 1.0 1.1 1.2 1.3 1.4 I.e 1.6 1.7 1.8
<'0,FLOW-0 CFSI
N
r'0 >-
0
Z
lU
::J !Sa
lU
0::
LL.
VELOCITY DISTRIBUTION (CFS)
Figure V-10.Frequency distribution of cell velocity over upwelling areas in Upper Side Channel 11 at
site flows of 5 and 50 cfs.
j j J I J J I •J !,)I I J I
"'J -1 -1 .
10090
SLOUGH 2!
Habitat Duration Curve
20 30 40 50 60 70 80
PERCENT TIME EQUALED OR EXCEEDED
1t5 ,000 .....
13,000
IIPOO
<C 9,000
:::t 7,000~
t5,OOO
3.000
1,000
t
60 70 eo 90 100 0 10
SLOUGH 21
flow Duration Curve
20 30 40 50
PERCENT TIME EQUALED OR EXCEEDED
10
1100,
1000-1
900
~800
o 700
~600
~t500
0400
it 300
Z
100
o~.'7 ,iii ,iii ,iii ii'iii
o
10090
UPPER SIDE CHANNEL 1/
Habitat Duration Curve
20 30 40 50 60 70 80
PERCENT TIME EQUALED OR EXCEEDED
10100°9080
UPPER SIDE CHANNEL "
flow Duration Curve
20 30 40 50 60 70
PERCENT TIME EQUALED OR EXCEEDED
10
15.000
13.000
IIPOO
<C 9,000
;:j~7.000
5.000
3.000
~,iii -;-i ,r iii iii iii ,i :,000 ~iii iii f I I I
-<
I
N
W 1100
1000
900
U)800IL
0 700
~600
~t500
0 400..J
IL 300
200
100
C
Figure V-II.Flow and habitat duration curves for spawning chum salmon by habitat categories.
1100
1000
900
(I)800
LL
0 700
z 600-
~500
0 400
...JlL.300
200
100
°I
°/0
SLOUGH 9
Flow Duration Curv ..
20 30 40 50 60 70
PERCENT TIME EOUALED OR EX~EDEO
15,000
13,000
11,000
<II:9,000
:::l 7,000~
5,000
3,000
1,000
t
80 90 100 °10
SLOUGH 9
Habitat Duration Curve.
20 30 40 !SO 60 70 80 90
PERCENT TIME EQUALED OR EXCEEDED
100
'=--';
S.....f""
<
I
r0
.p
10090
SIDE CHANNEL ZI
Habitat Duration Curv ..
20 30 40 !SO 60 70 80
PERCENT TIME EQUALED OR EXCEEDED
15,000
13,000
11,000
-e 9,000
:::l 7,000J:
5.000
3,000
',000
~'"
80 90 100 0 10
Sloe:CHANNEL 21
Flow Duration Cur.,.,
20 30 40 50 60 70
PERCENT TIME EOUALED OR EXCEEDED
10
1100
1000
900
(I)800
LLo 700
z 600
~500
o 400
...J
lL.300
200
100~;=:o ii'J 'Iii •Ii ii'i ,to
Figure V-II (Continued).
J J .J.J I I J J .j ,.1 !J J
-
-
r-
i
changes in their respective WUA indices associated with the 30 and 70
percent exceedance values.Category III sites,which are generally
breached\at a mainstem discharge of 10,000 cfs,reflect the influence
of mainstem discharge throughout the spawning period.
ltearing Salmon
l~li crohabitat Preferences.Fi e1d studi es,conducted by ADF&G to
determine the seasonal movement and habitat requirements of juvenile
chinook,chum,cohti,and sockeye salmon in the middle Susitna River,
indicate that juvenile chum and chinook salmon are the most abundant
salmon species that rear in side slough and side channel habitats.
duvenile coho salmon rear predominantly in tributary and upland slough
habitats.The few sockeye juveniles rearing in the middle Susitna
Ftiver are most commonly found in upland slough habitats.By early
summer (end of June)most juvenile chum salmon have outmigrated from
middle Susitna River habitats,and a large inmigration of chinook fry
occurs from natal tributaries.These immature chinook redistribute
into side channe 1sand side sloughs duri ng the rema i nder of the
summer.With the onset of fall and colder mainstem and side channel
water temperatures,chinook juvenil es appear to move into the warmer
\lIater associated with upwelling areas in side slough habitats to
overwinter (Dugan et al.1984).
Rearing habitat is commonly evaluated using three·variables:'depth,
velocity,and cover (Wesche and Rechard 1980;Boyee 1982).Habitat
suitability criteria have been developed by ADF&G to describe the
preferences of juvenile chum and chinook salmon for these microhabitat
variables.Habitat suitabil ity criteria developed by ADF&G indicate
that water depths exceeding 0.15 feet provide optimal conditions for
Y'earing chinook (Suchanek et al.·1984).This compares well with
Burger et al.(l982),who found chinook using depths between 0.2 and
10 feet in the Kenai River.
V~25
Cover is used by juvenile salmon as a means of avoiding predation and
obtaining protection from high water velocities.Instream objects,
such as submerged macrophytes,1a rge substrate,organi c debri s,and
undercut banks provide both types of shelter for juvenile salmon
(Bjornn 1971;Bustard and Narver 1975;Cederholm and Koski 1977;
Burger et a1.1982).One significant finding of the ADF&G field
studi es is that juveni 1e chi nook a re apparently attracted to turbi d
water for cover.Juvenile chinook were commonly found in low-velocity
turbid water (50-200 NTU)without object cover,but were rarely
observed in low-velocity,clear water (under 5 NTU)without object
coverl (Suchanek et al.1984).The influence of turbidity on the
distribution of juvenile chinook in side channel habitats was so
pronounced that different habitat suitabil ity criteria for velocity
and object cover were developed by ADF&G for both clear and turbid
water conditions (Figs.V-12 and V-I3).
These criteria curves assign optimal suitability values to velocities
between 0.05 and 0.35 fps for turbid water,and between 0.35 and
0.65 fps for clear water.Literature value,s typically indicate that
optimal velocities for juvenile chinook in clear water are less than
0.5 fps (Burger et al.1982;Bechtel 1983;P.Nelson,pers.comm.
1984).The criteri a presented by both Bu rger et a 1.(1982)and
Bechtel (1983)(Fig.V-14)can be considered comparable to ADF&G's
criteri a for juvenil e ch i nook i nsofa r as the Burger and Bechtel
criteria were developed for juvenile chinook (under 100 mm)rearing in
1 ADF&G selected 30 NTU to distinguish between clear and turbid
water conditions (Suchanek et al.1984).This is recognized as a
reasonable preliminary threshold value.However,because of the
limited number of data points that are available to define
juvenile chinook behavior at turbidities between 5 and 50 NTU and
above 200 NTU,turbi dity ranges will be parentheti ca lly expressed
in our discussion of juvenile chinook behavior in clear (under 5
NTU)and turbid (50 to 200 NTU)water conditions.Turbidity
ranges may be further defined in field studies.
V-26
-
....
0 •••])1 l C -·l 1
SUITABILITY INDEX
3.02.5
0.42
1.0
1.0
/.0
0.80
0.60
0.38
0.25
0.15
0.07
0.02-
0.0/
0.0
Turbid
2.0
018
0.28
0.57
f .0
1.0
1.0
0.68
0.44
0.25
0.18
0./2
0.06
0.0
Clear
LEGEND
___Turbid
CI ••r
1.5
0.0
0.015
0.20
O.M
0.50
0.65
680
1.10
lAO
1.70
2.00
2.30
2.60
Velocity
Clear water less than 5 NTU
Turbid water 50 to 200NTL
1.00.5
0.4
0.2
0.6
1.
0 11--'\,
I \
I \,\
I \0.8 -I,\
I \
\
\
\
\
\
\
\
"
""""'.......
.......~:......:.:::~::::.:::...=-_7:~~--..~I......-----rI------,---(;;---7;'~I0.0 -I I
o
)(
UJ
C
Z
)0-
I--<
..J
I
!
N
---J
-=>
U)
I
VELOCITY f.p.B.
Figure V-12.Velocity criteria for juvenile chinook in clear and turbid water.
LEGEND
t2J -Clear
_ -Turbid
Percent Cover
0.1 0-5
0.2 6 -25
0.3 26 -50
0.4 51 -75
0.5 76 -100
II1IIIIIJIll,.
..
pi
pi
I.
~,.b=:::::vr:8::
pi ~~•~•Ii ,..~
~t::::~~f::.:~..I~'"1IIf::.:III .~~~%~%~~~~~~~~
%,..~~....§§~..•~..~~~~~v ~~~~~~~~~.~~I·I ~~~~~.~~.~~~~~~~~~~~~~~~~~~~~~
%/~~~~~~~~~~%f::.:~%t::::~~~~~~~~~~~~~~~~~%~~~%~%%y%~~~%v./~~~8%_~~~/V.%~~y~~~~~~//V.%~~~%~~v~~~~%t::::~~~~%%~yv.~%~%~~~~~~/%~%~~%~~~~%~%~~~~~~~%~%%%~yv.y %%~%~~~%%%%~%%%~%~~~~~:::::%~~~~~v:%~~~~~~~%~~%~~~~y~~~~~~~/~~~~~~f::.:~~%%%~~~%%/%/~%V ~%~~~/v./~y ~L /'/'/;;.-:r::.;;:::2:1/:,..--/
•..
..
..
1.0-
00-f!21'IzJ"'dlb~H?Y4<1/~<r£4<K"6rf6l6.f1fT :'.HI'I
.o.l---...o~o.1 ;o.fio.1 +oao.l--o.1I0.,---0.ao.,:0.110.1 ---..O.II'O:I----+-O.lIO.I----JOo'O./l
x OB-w .
oz
>-
I-0.6-
....J
(J)
;:!
~
if)0.4-
I-
~
(J)
«2-I O.
<
I
N
00
2 3 4 5 6 7 8 9
No Cove r Emergent Aquatic Debris and Ol/erhonqino Undercut Laroe Rubble Cobble or
Vegetation Vegetation Deadfall Riparian Bonks Grovel 3"-.5"Bouldera
over 5"
PERCENT COVER by COVER TYPE
Figure V-13.ADF&G cover criteria for juvenile chinook in clear and turbid water conditions.
)t eel J J J J J J J
1 --~'l ")J 1 ~~l --j '~._"J 1
3.02.~2.0I.~
I Bura.r .t al.ue2SI5-S0Ilm
-~aura.r .t ~1.1 oe2 151-100",
,-'-·-·Bechtel 1983
i LEGEND i
.-
1.0
\
\
\'-.
o.~
\
~\
'.\
'.\
\,
'\,
"
"
\"
'\
"
"'"
"""
1.0"'"..,...,...-'\•
0.0 ,Iii -.,.,...I i
o
0.2
0.8
X
L&Jo
Z
>-0.6....--J-~....-:J
C/)0.4<
I
N
<.0
VELOCITY f.p.s.
Figure V-14.Velocity suitability criteria for juvenile chinook in the Kenai and Chakachamna rivers,
Alaska (Burger et al,1982 and Bechtel Civil and Minerals 1983),
large glacial rivers in Alaska.Although the chinook criteria from
the literature were developed from data collected in clear water (less
than 30 NTU),they are more simil ar to the Susitna River velocity
criteria for turbid water (50-200 NTU).The apparent reason for this
discrepancy is the difference in field methods used by ADF&G and the
other investigators.
Mean column velocities were measured by both ADF&G and other investi-
gators to develop habitat suitabil ity curves for juvenile chinook.
However,the location at which the mean column velocity was measured
relative to the apparent locations of juvenile chinook were different.
ADF&G reported the mean column velocity at the midpoint of a six-foot
by 50-foot cell (mid-cell velocity)regardless of the location of fish
within the cell.The velocity criteria developed by Burger and
Bechtel are based on mean column velocities measured in the immediate
vicinity of individual fish observations or captures (point velo-
cities).
Assuming that immature fish in clear water are more likely to be found
along 'stream banks (where lower velocities and cover are generally
more available),the practice of measuring mid-cell velocities a
minimum distance of three feet (one half the width of the ADF&G sample
cell)from the streambank would result in slightly higher mean column
velocities being measured than if point velocities had been measured.
It is understandable that the 0.35 to 0.65 fps velocity range selected
by AOF&G as being optimal for juvenile chinook is slightly higher than
the 0 to 0.5 fps velocity range selected by other investigators.
However,it should not be assumed that low velocities (less than 0.35
fps)are unimportant to rearing chinook salmon.Consequently,the
optimum velocity range of the IFR clear water suitability criteria
were extended to include velocities between 0.05 and 0.65 fps
(Fig.V-IS).
Juvenile chinook do not associate with object cover in turbid water
(50-200 NTU)as much as they do in clear water (Suchanek et al.1984).
Rather,they are randomly distributed in low velocity areas with
V-30
-
VELOCITY SUITABILITY CRITERIA FOR JUVENILE CHINOOK SALMON
SUITABILITY (Sv)
Velocity Clear Turbid
3.02.5
0.42
1.00
1.00
1.00
0.80
0.60
0.38
0.25
0.15
0.07
0.02
0.01
0.00
2.0
0.42
1.00
1.00
1.00
1.00
1.00
0.68
0.44
0.25
0.18
0.12
0.06
0.00
LEGEND
---Turbid
---Clear
1.5
Clear water less than 5 NTU
Turbid water 50 to 200 NTU
0.00
0.05
0.20
0.35
0.50
0.65
0.80
1.10
1.40
1.70
2.00
2.30
2.60
VELOCITY (ftlsec)
1.00.5
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
\
"-,,-
"-"-"-"-"-
"-"",-
'-"....................
............
........._---
0.8
1.0
-.,.
0.6!!!.
>-~
:::i
CD
~
:5en 0.4
I"'"
I
""'"
0.2
I"""
0.0
a
-
".....
Figure V-I5.Velocity suitability criteria used to model juvenile
chinook habitat (WUA)under clear and turbid water
conditions in the middle Susitna River (Steward 1985).
V-31
little or no object cover.In these low-velocity turbid areas,it is
quite likely that mid-cell velocities measured three feet from the
streambank differ little from point velocities measured in
microhabitats along the shoreline.that would be inhabited by juvenile
chinook in a clearwater stream.Therefore,it is not surprising that
the a to 0.4 fps velocity range selected by ADF&G as being optimum for
juvenile chinook in turbid water differs little from the 0 to 0.5 fps
velocity range selected by other investigators using point velocity
measurements rather than mid-cell velocities as their data base.
It can be inferred from the ADF&G habitat suitability criteria that in
low-velocity water «0.4 fps)juvenile chinook do not require
protection from water currents and are more likely to be found within
the water column away from object cover if the water is turbid (50 to
200 NTU)than if it is clear (less than 5 NTU).At velocities greater
than 0.4 fps,the distribution of juvenile chinook in turbid water
is more strongly influenced by velocity.When velocities exceed
1.0 fps,object cover is probably as important to juvenile chinook in
turbid water as it is in clear water.However,since these young fish
probably cannot visually orient in turbid water,they cannot make use
of object cover that may be available and are,therefore,redistri-
buted in microhabitats by velocity currents.
Whenever mainstem discharge recedes sufficiently for side channels to
become nonbreached and the turbid water to clear (due to the influence
of local runoff and/or groundwater inflow),juvenile chinook often
move from formerly occupied low-velocity turbid water pools to small
clearwater riffles near the upstream end of the site.Given the high
suspended sediment concentrations that occur naturally in side channel
habitats,interstitial spaces between streambed particles in low
velocity areas are generally filled with fine glacial sands.Thus,at
low mainstem discharges when these side channels are not breached and
water at the site has cleared,the most likely place to find
interstitial spaces not filled with fine sediments is in riffle areas
that were subjected to relatively high velocities when the site was
breached.Such riffle areas generally occur near the head of the side
channel.
V-32
-
""'"
....
.....
From the preceding discussion,it can be concluded that velocity and
cover are the two most important abiotic microhabitat variables
influencing juvenile chinook rearing habitat.Of the two,cover
appears more influential.Although offering no protection from
velocity,turbid water appears to provide juvenile chinook adequate
cover if velocities are less than 0.4 fps.In clear water,juveniles
~lenerally seek concealment within interstitial spaces among streambed
particles.These interstitial spaces also provide enough protection
from velocity that juveniles are frequently found in areas possessing
velocities between 0.35 and 0.65 fps (Suchanek et al.1984).
Based on the foregoing discussions,the clearwater cover and depth
criteria developed by ADF&G for chinook have been adopted for use in
the IFR analysis.However,the ADF&G velocity criteria for juvenile
chinook in clear water have been modified such that the optimal
velocity range extends from 0.05 to 0.65 fps rather than 0.35 to 0.65
fps (refer .Fig.IV-IS).As velocity increases above 0.65 fps,the
habitat suitabil i ty decreases in accord with the ADF&G cl earwater
criteria.
In turbid water habitats,the ADF&G depth and turbid water velocity
criteria are applied.However,the ADF&G turbid water cover criteria
were modified by multiplying the clearwater cover suitability values
for each cover type by a turbidity factor.This turbidity factor is
the ratio between the fitted mean catch per cell in turbid and clear
water for corresponding cover categories (Table V-3).
V-33
Application of these turbidity factors increases the suitability of
a microhabitat area if 50 percent or less of its surface area has
object cover.Turbidity has no discernible influence on cover if 51
to 75 percent of the microhabitat area possess object cover and
slightly decreases habitat suitability if more than 76 percent object
cover is present (Fig.V-16).The decrease in suitability of the
higher percent cover categories in turbid water is considered to
reflect the inability of juveniles to visually orient themselves in
turbid water (>50 NTU)and fully utilize the available cover.
Because the turbid water suitability values calculated for the "emer -
gent streambank vegetation"and "no-cover"types were unrealistically
low (approximately 0.04),the value,0.30,was chosen for these cover
types under turbid water conditions.Th-is seemed appropriate because
0.30 was the value calculated for the majority of other cover types
under turbid water conditions when zero to 5 percent object cover was
available under clearwater conditions.
Habitat Availability.Figure V-17 compares WUA indices forecast using
both the ADF&G and the modified velocity criteria for juvenile chinook
rearing at Side Channel 21 and Upper Side Channel 11.Increasing the
range of low velocities suitable for juvenile chinook in clear water
at these study sites did not significantly affect the shape of the WUA
response function preViously forecast by ADF&G.This is attributable
to the poor cover conditions associated with low-velocity areas in
these sites under natural conditions.The most notable changes
occurred where low-velocity water is more likely associated with
larger substrates in the mid-channel zone or with streambank cover at
high flows (Upper Side Channel 11).
Figure V-IS presents WUA indices forecast for juvenile chinook using
cover criteria for low and high turbidity conditions.Identical
habitat response curves are forecast under low-turbidity conditions
because the ADF&G clearwater cover criteria remains unchanged.
V-34
-
.1.0-
CJ 0.8-
oz
>-
I--0.6-
..Jas
t!
.::)
(j)0.4-
J-~
CD
~0.2-
<:
I
W
U1
]
~~l:%t%:~l:%~y ~~~~~~~~~j;ir;~r;~~1~1;~~~~v.~V 'lJo'v~'"t;::-~~§J~r7 /~~r.r:E;,;::
.~~~~~~~l~~f;;t?
..j ~I ~f%~~~%~~-~~~~~~~~~~%~~~~.~~~~~I~~~
J ~~~~~~%t%:~~~~:%%l:%~~~~%v~~~~~~~~~~~~~~~~~~~~~~~~-~~~~~~~.~~~~~~7.~~~~~%%~~~~~~~~~~~~%~~'i %%Y~v.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~l:%~~~%~~Z :%%~~~:%%l:%%~'l ~~~~~~@ ~~~~~:%~~7~/~~~~~~~~~~~~~~~~~~~~v.~~~~~~~%V~Z ~~~v.:%~~~~~~~~~~~~~~~~~~~~b~~~~~~~r;~/~~~~~~~~~~~~~'l ~~%~~~~V~~0.0
O.I--'O.!OJ "'O.lSO.1 "'QlSO.'...0.150.1--.0.150..,.O'&O'I...-......O'IIO"-...O.&OJ--....O.lt
2 3 4 5 6 7 8 9
No Cove r Emergent Aquoti c Debris and Overhanging Und&rcut Large Rubble Cobble or
Vegetation Vegetation Deadfall Ri porian Bonks Grovel 3"-15"Bouldera
over 5"
PERCENT COVER by COVER.TYPE
Figure V-16.Revised cover criteria·for juvenile chinook in clear and turbid water.
1
LEGEND
~-Clear
_ -Turbid
Percent Cover
0.1 0-'5
0.2 6-25
b.3 26-50
0.4 51'-75
0.5 76 -100
UPPER SIDE CHANNEL 11
260200
-------------.••,180'100
10000 ~•••SITE FLOW (CFS!o
20000-'".......-<C
Wa:
C
16000
40000
<:
I -W '"Ctl .......-
c(30000
Wa:
<C
20000
SIDE CHANNEL 21
------------
260200100150
SITE FLOW (CFS)
60
10000 11-0--------::'~-----~~'-=-------....,...'--------,....---------.o i
Figure V-I7.Comparison between WUA forecasts using AnF&G low turbidity velocity criteria (solid line)and
modified low turbidity velocity criteria (dashed line).
,t B ":.J J t ~J j __J _,J •
1 "f c""~1 ~'""""l .)"~'J ..~·····1 ·~··-l 1 l )
SITE FLOW (CFS)
1600
Low Turbidity
400 SOD 800
SITE FLOW (CFS)
tOO
Sid,Chann,'tl
·0
20,000
15,000
150,000
45,000
40,000
1:'....",000........
octLIJ llO,OOO
a:::
-<
tOO 2'21\1751150
Low Turbidity
1215100u,5025
Upper Side Channel II
o
20,000
"15,000
50,000
~40,000.....
~315,000ex
IJJ 30,000
0::ex 215,000-
~".--....----__Ifilii'--.......~_
~---------
1400,too1000
High Turbidity
400
----.......-.-.....-----.-......--------
200
Side Chonnel 21
o
111,000
60,000
r 11&,000
;:=!lO,OOO'<46,000
~40,000
-<315,000
30,oao
215,000
'"20,000
IlI,OOO
10,000 11;---:r:'::---""'"':"!'-::----:-r'----,'r---""!"i----"....------.,
U&tOO11111&0
High Turbidity
Ita10076150215
Upper Side Channel II
a
150,000
415,000
10,000
;:--4 0,000.....
~3!l,000
«
IJJ 30,000
a:ex 215,000
20,000
1!l,OOO
<:
I
W
---J
SITE FLOW (CFS)SITE FLOW (CFS)
Figure V-lB.Comparison between WUA forecasts using ADF&G (solid line)and modified cover criteria
(dashed line)for juvenile chinook.
Application of the modified turbid water cover criteria results in
approximately a 25 percent·reduction in WUA indices from the ADF&G
forecasts.However,the bas ic shape of the habitat response curves
remains unchanged.
Under project operation,the larger suspended sediments (sands)that
are currently transported by the river are expected to settle out in
the reservoirs.Without continual recruitment of these sediments into
habitats downstream of the reservoirs it is anticipated that the finer
material presently filling interstitial spaces among larger streambed
particles will be gradually removed.The effect of an increase in
cover suitability resulting from the removal of these sediments was
simulated by increasing the percent cover at two study sites one
percentage category and recalculating WUA indices for juvenile
chinook.This simulation provided increased WUA indices at Upper Side
Channel 11 and Side Channel 21 of approximately 40 to 60 percent
depending upon whether the clear or turbid water suitability criteria
were applied (Fig.V-19).
Rearing habitat for juvenile chinook under low-and high-turbidity was
forecast for Side Channel 21 and Upper Side Channel 11 using a
combination of the modified velocity,and cover criteria in
conjunction with ADF&G criteria for depth,velocity and cover
(Table V-4).The respective WUA forecasts are compared to total
surface area in Figure V-20.The upstream berms at these sites are
overtopped by mainstem discharges of 9,200 and 13,000 cfs,respec-
tively.Low turbidity exists at these sites whenever the mainstem
discharge is insufficient to overtop the upstream berms.The same
relationship exists between WUA indices and mainstem discharge when
low turbidity prevails.Whenever the sites are overtopped and high
turbidity exists the revised model forecasts less WUA.Turbidity has
a lesser effect on increasing WUA indices at the Side Channel 21 site
than the Upper Side Channel 11 site because less favorable velocities
typically exist at the Side Channel 21 site.
V-38
-
-
-','~<"-'l '--I '----j 1 J ,j .,1 1 £,"--'}l l }}l
-.....---"----'-------r
~
Uppe r Side Chonn.'II
'400
--
12001000
Low Tllrbldit,
................--
400 lIOO 800
SITE FLOW (CFS)
200
Sick Chonnel 21
\l
I \
........""--................."""..................
o
IllPOO
10.0
001 I I I I i I I
tO,OOO
lII.ooo .
40,000
1I0,con
211.000
ao,ooo
411,000
t<+-~
'I
It!
tI:
0(
2211200/1ll
Low Turbidity
/llO1&100 126
SITE FLOW (CFS)
lIO•2ll
40,000
3&,000
i:'50.000~
~~
0(18,000
u.J
0::20,0000(
IS,OOO
10,000
:1,000
a
0
......------......--...
~---------,-------
HIgh TurbldltvSIdeChannel21\
\-\--~--'"_...._---------
~O,ooo
110,000
411.000
....-,",opoo....
~3ll,ooo
<CIt!50,000
II:
<C tll,ooo
High TurbidityUpperSideChannelII
~\'-,........
40,000
58,000
,c;-
~32,000
--"
~~8,OOO
il:
>tf.24,000
l'O,uOO
<:
1
W
o.D
18,000 111,000
12,000
f I i I f iii i i
/0,000,1T----"'"1".----.,.,----.,.,----.,.,----.,.,----.,..,----.,.,
o fa ao 111 100 Il!ll
SITE FLOW (CFS)
1110 1111 200 ttll o 200 400 1100 800
SITE FLOW (CFS)
1000 lilOO '400
LEGEND
- -WITH REDUCED SEDIMENT
-WITHOUT REDUCED SEDIMENT
Figure V-19.Simulated effect of reducing fine sediment deposition at two study sites.
100000-'"-........
cwa:c
&0000
UPPER SIDE CHANNEL 11
TOTAL SURFACE AREA
t--t
<
I
-l::>.o
ADF&O WUA
~~-----~-~---~---~-~--~~-~--~,.REVISED MODELl.._---
0'.'iii
10000 14000 18000 22000 26000
MAINSTEM FLOW (CFS)
SIDE CHANNEL 21
-N.........
ottwa:
<t:
200000
100000
TOTAL SURFACE AREA
~__:::-=:.ADF&O WUA
---..*-
REVISED MODEL ----------------a ,,,,•i
5000 10000 18000 20000 28000 30000
MAINSTEM FLOW (CFS)
Figure V-20.Comparison between WUA forecasts using ADF&G and revised rearing habitat model.
J I }J -1 s J t ,)
Table V-4.Habitat suitability criteria used in revised model to
forecast WUA for juvenile chinook salmon under low and
high turbidities.
Low Turbidity «30 NTU)
ADF&G Cover Criteria
ADF&G Cover Criteria
Revised Velocity Criteria
High turbidity (>30 NTU)
ADF&G Depth Criteria
Modified Cover Criteria
ADF&G Velocity Criteria
-
r
!
r
Given the habitat suitability criteria developed for juvenile chinook
and typical middle river conditions,depth of flow is a relatively
inconsequential microhabitat variable unless it is less than 0.15
feet.Thus,the general shape of habitat response curves for juvenile
chinook is determined primarily by the interaction between cover
and velocity.Because juvenile chinook salmon in the middle Susitna
River use naturally occurring turbidity levels as a form of cover,
notable increases in WUA are caused by the breaching of a clearwater
study site by turbid mainstem flow.The magnitude of the WUA increase
is proportional to the increase in wetted surface area possessing
suitable velocities.
The relationship between WUA and wetted surface area is plotted as a
flow dependent percentage in Figure V-21.At higher mainstem
discharges a lesser percentage of the total wetted surface area is
available as rearing habitat.This is attributable to wetted areas
w'ith suitable velocities for rearing fish becoming available at a
lesser rate as discharge continues to increase;a common occurrence in
well-defined steep gradient channels.The most efficient use of
streamflow to provide rearing habitat appears to occur immediately
following overtopping of the site when the flow is turbid and a
large percentage of the total wetted surface area is associated with
low velocity flow.
V-41
10,000 12,000 14.000 16.000 18.'000 20;000 22;000 24;000 26;000
.MAINSTEM FLOW.GOLD CREEK (CFS)
8,000
LEGEND
Upp.r Side Channel II
---Side Channel 21
",...
.""
.""--'""-
5
o~I I I I I I I I I I
6,000
10
~-,]~----~~I~._
0
G)
l-
e:(
eg....
I-
::J
(I)
"e
<..
I ...
.Po>;N
G)
01
0...
j
0
~a..
Figure V-21.Percent of total wetted surface area providing WUA for rearing chinook at Side
Channel 21 and Upper Side Channel 11 .
J ,I .~I J ,8 •.J I I .1 I ~J
-
,-
I
I ,..
-
.....
.....
i
VI.SUMMARY
This section summarizes the relative importance of the various phys-
ical processes and habitat variables discussed in Sections IV and V
with regard to the primary evaluation species and evaluation periods
identified in Section III.The major conclusions obtained from a
subjective evaluation of naturally occurring physical processes is
presented,as well as,a discussion of some inherent project-induced
changes to these processes.Understandi rig the nature and general
magnitude of these project-i nduced changes shoul d provi de a sound
technical basis for selecting streamflow and stream temperature
regimes to avoid or minimize negative effects,and maximize beneficial
effects,of the proposed Susitna Hydroelectric Project on fish
habitats within the Talkeetna-to-Devil Canyon river segment.
Influence of Streamflow on Habitat Types and Other Variables
Six aquatic habitat types have been identified based on similarities
in morphologic,hydrologic,and hydraulic characteristics (ADF&G,Su
Hydro 1983a;Kl inger and Trihey 1984).The surface area of some
habitat types such as upland sloughs,tributaries and tributary mouths
are relatively insensitive to variations in mainstem discharge.
However,both the wetted surface a rea and habitat quality of other
habitat types such as the mainstem and side channels,respond directly
to variations in mainstem discharge.In addition,the type of aquatic
habitat which occurs at some locations (specific areas)is also a
function of mainstem discharge.Such an example is the transformation
of turbid water side channel habitat to clear water side slough
habitat as mainstem discharge decreases (Klinger and Trihey 1984).
Because of these marked responses of aquatic habitats to changes in
mainstem discharge,the streamflow regime of the middle Susitna River
is considered the primary driving variable that controls habitat
alvailabil ity.Important descriptors of mainstem discharge are the
magnitude,frequency,duratior;l,and seasonal ity of streamflow events.
Microhabitat variables,which respond to variations in streamflow,and
VI-1
whi ch i nfl uence the quality of fi sh habitat are depth,velocity,
channel structure,substrate composition,upwelling,water temper-
ature,suspended sediment,turbidity,and dissolved organics and
inorganics.Many of these variables are themselves interrelated.
Understanding the cause-effect relationships between these variables
and quant ifyi ng the magnitude of project induced changes to them
provides a technical basis for estimating both the beneficial and
adverse effects of the proposed project on fish habitat and
populations.
Regi ona 1 c1 imate causes seasonal and annual va ri ati ons in streamflow
and stream temperature.Basin topography and geology in concert with
regional climate determine runoff and water quality patterns,channel
morphology,and streambed composition.For the middle Susitna River
channel morphology and,to a large degree,streambed composition can
be considered constants (R&M 1982a;Univ.of Alaska,AEIDC 1985b)but
streamflow,stream temperature and water quality vary both seasonally
and annually.
The relationship between air temperature and water supply determines
the seasonal response of streamflow,water temperature and water
quality.Annual variations in basin precipitation and climate account
for year-to-year fluctuations with cyclic variation of air temperature
being the primary cause of seasonal differences.Summer drought is
usually moderated by streamflow originating from glaciers (which cover
about 290 square miles of the upper Susitna Basin)and from three
large lakes in the Tyone River drainage.Because glacial flow results
in high turbidities.and suspended sediment concentrations during
summer,the water quality of rna i nstem i nfl uenced habitats changes
markedly with the seasons.
High streamflows reshape channel geometry,which at lower discharge
1eve 1s contro 1s s ite-specifi c hydrau1 ic conditions.Medi an summer
streamflows typically exceed the mean annual discharge by a factor of
two and transport large amounts of suspended sediment.The associated
VI-2
-
-
-
-
-
-
high velocities,turbidities,and abrasive action of the suspended
sediments are considered limiting to the colonization of the streambed
by algae and aquatic insects,which generally provide an important
food source for fish.
Streamflows and stream temperatures during winter play an integral
Irole in middle Susitna River ice processes which directly affect
channel structure,shoreline stability,and the general quality of
\vinter fish habitat.River ice also affects instream hydraulics,most
notably by constricting the channel,reducing velocity,and increasing
river stage.This increase in water surface elevation during winter
has both positive and negative effects on fish habitat.Higher water
surface elevations during winter are considered important for raising
"local groundwater elevations,thereby maintaining upwelling in slough
an side channel areas.These upwellings provide a source of
relatively warm water (2-3°C)throughout winter (Trihey 1982;ADF&G,
Su Hydro 1983c)which is considered essential for the survival of
"incubating salmon eggs and overwintering fish.However,if river
stage increases enough to overtop the upstream berm of the slough or
side channel,then near aoc water would flow from the mainstem into
these sites,negating the thermal effect of upwelling and greatly
reducing the value of upwelling areas as winter habitat.
River stage (discharge)is important during summer with regard to
controlling access to fish habitat in side channels and sloughs
located along the flood plain margin.Because of the complex
multi-thread channel pattern of the middle Susitna River,changes in
rna i nstem water surface el evati on strongly i nfl uences the amount of
watered and dewatered channel area as well as the relative percentages
of clear and turbid water surface area (Klinger and Trihey 1984).
Seasonal Utilization of Middle River Habitats
r1ainstem and side channel habitats are predominantly used as migra-
tional corridors by adult and juvenile salmon.Adult inmigration
VI-3
begi ns in 1ate May and extends to mi d-September.Juvenil e outmi-
gration occurs from May through October.A 1imited amount of chum
salmon spawning occurs at upwelling areas along shoreline margins in
these habitats (Barrett et al.1984),and chinook juveniles use
low-velocity areas for rearing (Suchanek et al.1984).Several
species of resident fish also use mainstem and side channel habitat
during both summer and winter (Sundet and Wenger 1984).The more
important species appear to be rainbow trout,Arctic grayling,and
burbot.
Si de 510ughs provi de important spawning,rearing,and overwi nteri ng
habitat.One prominent physical characteristic of this habitat type
is the influence of upwelling groundwater,which maintains clear water
flow in these habitats during periods of low summer mainstem discharge
and open leads during winter.Approximately half of the chum salmon
(5,000)and all of the sockeye salmon (1,500)that spawn in the middle
Susitna River do so in side slough habitats (Barrett et al.1984).
Most chum and sockeye spawning activity occurs between mid-August and
mid-September.Upwelling attracts spawning salmon and provides
incubation conditions that result in high survival rates (Vining et
ale 1985).Fry begin to emerge in April,and rear near these natal
spawning areas until June (ADF&G,Su Hydro 1983e).Chum fry out-
migrate to marine habitats during June and early July.Juvenile
chinook enter side slough habitats in August and overwinter until late
spring,when they begin their outmigration to marine habitats.
Upland sloughs provide summer rearing and overwinter habitat for
juvenile coho and chinook salmon (Dugan et al.1984).Sockeye
juveniles generally move into upland sloughs during June,but many
leave prior to the onset of freeze-up.A 1 imited amount of spawning
by chum salmon also occurs in this habitat type (Hoffman 1985;Barrett
et al.1984).Tributary mouths provide a small amount of spawning,
rearing and overwintering habitat.Small numbers of pink,chum,and
chinook salmon have been observed spawning in tributary mouth habitats
(Barrett et al.1984)and juvenile chinook and coho salmon may be
found in these habitats throughout the year (Dugan et al.1984).
VI-4
-
-
-
-
-
-
Evaluation Species and Periods
Seasonal habitat requirements are species-and 1 ife stage-specific.
Evaluation species were selected on the basis of their importance to
commercial and sport fisheries (refer Section III),and the potential
for project constructi on and operation substanti ally a Heri ng thei r
E~xisting habitat.The primary evaluation species and life stages are
chum salmon spawning and incubation,and juvenile chinook salmon
j"earing.Since biological activity,physical processes,and habitat
conditions vary seasonally,the year was divided into four evaluation
periods.These periods were selected to best accommodate the natural
timing of the four principal freshwater 1ife stage activities of
Pacific salmon (spawning,incubation,overwintering,and summer
rearing)in the middle Susitna River (Fig.VI-I).
JUthough portions of the evaluation periods overlap,the habitats
occupied by overlapping life stages as well as their habitat
requirements differ sufficiently to warrant separate analyses.To
faci 1 itate i ntegrati ngperi ods of bi 01 ogi c activity with the standard
time step used in the reservoir operation and various streamflow
models,evaluation periods are defined coincident with water weeks
(Table VI-I).Water weeks begin October 1 and consist of 51
consecutive 7-day peri ods.The fifty-second week (September 23-30)
contains eight days,and February 29 is omitted.
Table VI-I.Evaluation periods as defined by water weeks.
,-
i
..?pecies Life stage Evaluation period Water Weeks
Chum Spawning August 12 to September 15 45 through 50
Chum Incubation August 12 to March 24 45 through 25
Chinook Overwintering September 16 to ~lay 19 51 through 33
Chinook Summer rearing May 20 to September 15 34 through 50
VI-5
--_.,---------------------------------------
I ~
Ji
N FEB MARl APR MAY JUN JUL AUG SEP OtT NIV DEC REMARKS
~I I -I I I I I I I----~!---
1M -_.----R"SS----S~S--~---P --
S --RS
:::E
UI
~
G)I 1--...............~....-........IeCS (~S·-;s ~.......--1-...-Z
~..............................·RS ..............'"
:::E 1-----1--»~SSR-8 ----1---1---------~-------------------
R 1--~-----CS
~--------PS
-----~---t-_K_~!JIG 1".11.'.,Ht.<~-------fl'l'iw ''0 .,..."'l'~\
OM ------RS f"CI~tf44.I"...'.trt_~--CS ..,'Ion .._II ..-------~--P ~.
---I--KS ...---~1M S
---PS CS
-----KS
5 1----SS----I--CS
>----PS
a:1--KS K&--~---------------....-------------''''''c.\ItI.tIOIl f.,._
~..1-------1-------CS PS cel s---1-------------lfl.t Ion d.f...'1"-
:;)fJ..t .......ld........c"
!!!...-------------55 Sl ~---------....4 1."•••,..
a::
to-
R -------------...----KSS ~------------------
OM --------CS PS
....---------------KS 55
---P~CS1M---"'-AS
-1---.-.-~S-eSS-_..----AS
G)
:t:11'tC-'IoIb.t 1on ,.,..-
0 ._._...-._..PS CS~~._.1-.-.-.1-.-.-.-.-In..IIOl"d.'."
::l I ..-..-...._._..-._....-.,b..t_~lIPli'd
0 1-------------les RS it---------------&arCh MId l.t.
.J
....
Cl)~-_.--_.-------.-----~§SSI ~---1-------~~--1-------A I------CS---
OM --------I--CS.-._..-·_·-PS
1----------I--KS SSRS
-
....
-
-
-
-
RELATIVE USE
-----HIGH
.-.-._.-MEDIUM
.............LOW
KS CHINOOK SALMON
SS COHO SALMON
CS CHUM SALMON
PS PINK SALMON
RS SOCKEYE SALMON
BASED PRIMARILY ON ADF&G FIELD DATA
.1M IN MIGRATION
S SPAWNING
I INCUBATION
R REARING
OM OUT MIGRATION
-
Figure VI-I.Phenology and habitat utilization of middle Susitna River
salmon in mainstem,tributary,and slough habitats (adapted
from Woodward-Clyde and Entrix 1985).
VI-6
",-
r
-
Relative Ranking of Physical Habitat Variables
Table VI-2 presents the results of subjectively evaluating the techni-
cal information presented in·Sections III through V within the
analytic structure of the IFRS model introduced in Section II.This
table summarizes the relative degree of influence that individual
physical habitat variables exert on aquatic habitats in the middle
Susitna River during each of the evaluation periods identified above.
The habitat-and evaluation period indices provided in Table VI-2 only
consider physical aspects of habitat quality and do not reflect the
important synergistic influences that biologic processes have on the
quality and productivity of aquatic habitats.Therefore,these index
va lues shaul d not be used to rank habitat types or eva 1 uati on peri ods
iin terms of their productivity.
The presence of upwelling water is the most important habitat variable
iinfl uenci ng the sel ecti on of spawni ng areas by chum salmon and it
significantly affects egg-to-fry survival rates (ADF&G,Su Hydro
1983c;Vining et ale 1985).Upwelling's importqnce is derived from
its associated thermal and water quality characteristics which provide
life support for the aquatic community during winter and to a large
E!xtent i nfl uence habitat qual ity duri ng the remainder of the year.
Table VI-2,Parts A and B summarize the influence of this physical
habitat variable on spawning and incubation for each habitat type.
Use of upwelling areas in mainstem and side channel habitats by
spawning salmon is limited by several factors.High sediment concen-
trations result in large volumes of sand being transported in close
proximity to the streambed,and mainstem and side channel streambeds
flenerally consist of large particles which are well-cemented by silts
and sands (R&M 1982a;ADF&G.Su Hydro 1983a).During August mainstem
stage is usually adequate to provide adult spawners access to
upwelling areas in mainstem and side channel habitats (Harza-Ebasco
1984g;Klinger and Trihey 1984),but,naturally declining water
VI-7
Table VI-2.Relative degree~1 of influence that phy~ical habitat variable~exert on the suitability
of middle Su~itna River habitat type~during the four evaluation periods.
Habitat*
Variable Mainstem
Side
Channel
Side
Slough
Upland
Slough
Tributary
Mouth -
(August 12 -March 24)
Mainstem flow
Upwelling
Substrate composition
Suspended sediment
Turbidity
Water Temperature
Habitat Index
Mainstem flow
Upwelling
Substrate composition
Suspended sediment
Turbidity
Water temperature
Ice proces~e~
Habitat Index
Mainstem flow
Upwelling
Sub~trate composition
Suspended sediment
Turbidity
Water temperature
Ice processes
Habitat Index
PART A:
-3
+1
-3
-1
o
o
-6
PART B:
-3
+1
-1
-1
o
-3
-2
-9
PART C:
-2
+1
-2
o
o
-3
-3
-9
Spawning (August 12 -
-3
Incubation
-2
+2
-1
-1
o
-3
-2
-7
Overwintering
-2
+1
-2
o
o
-3
-3
-9
September
+5
+2
+3
+1
o
o
+2
-1
+7
+2
+3
+2
o
o
+2
-2
+7
15)
o
+3
-2
o
o
o
+1
o
+3
-1
oo
+2
o
+4
o
+3
-1
o
o
+2
-1
+3
-1
+2
+2
o
o
o
+3
-1
+2
+1
o
o
-2
-2
-2
-1
+1
+2
o
o
+1
-2
+1
-
-
PART D:Summer Rearing (May 20 -September 15)
Mainstem flow -3 -2 +2 0
Upwelling 0 +1 +2 +2
Substrate composition -2 -2 +2 +1
Suspended sediment -3 -2 -1 -1
Turbidity +2 +2 0 0
Water temperature 0 0 0 0
Habitat Index -6 -4 +5 +2
-2
o
+2
oo
o
o
.....
-
*
Evaluation scale
+3 extremely beneficial
+2 moderately beneficial
+1 slightly beneficialonoeffect
-1 slightly detrimental
-2 moderately detrimental
-3 extremely detrimental
Typical conditions for the habitat type during the season evaluated.
VI-8
-
-!
I
l
.-
-
-,
I
-
surface elevatins during September limit spawning habitat quality in
some mainstem upwelling areas.Mainstem and side channel habitats are
are generally limited by velocity,except in isolated backwater
I ocati ons along streambank margins.These 1ocati ons usually possess
11 ow quality spawning substrates because of their tendency to
accumulate relatively deep deposits of fine sediments.
Exclusive of the major clearwater tributaries,spawning most fre":
quently occurs in side slough habitats where upwelling is prevalent
and other physical habitat conditions are suitable.Naturally
occurring velocities seldom limit spawning in side slough habitats.
However,side slough habitats are often limited by shallow depths,and
poor quality streambed composition.Shallow depths also cause passage
problems which inhibit spawning salmon from using upwelling areas in
upstream portions of the side sloughs.Periodic short-term increases
in slough flow are important for improving passage conditions (Trihey
1982;Estes and Vincent-Lang 1984c).These increases are principally
caused by overtopping events or by rainfall runoff.
Both i ncubati on and overwi nteri ng are adversely i nfl uenced by
natura lly occurr;ng col d water temperatures,river ice,and low
streamflows (refer Table VI-2,Part B and Part C).The presence of
upwelling groundwater creates favorable incubation conditions in
slough habitats and resulted in egg-to-fry survival rates up to 35
percent in 1983-1984 (Vining et ale 1985).Pools within the sloughs
generally provide adequate depth and water temperatures for juvenile
fish to overwinter.At times,side sloughs are overtopped during
\llinter as .a result of the mainstem ice cover formation (refer
Section IV).The influx of cold mainstem "water into side slough
habitats may reduce intragravel water temperatures and adversely
affect incubation rates and embryo growth.Overtopping also adversely
clffects overwintering fish.
The adverse influence of cold water temperatures is most pronounced in
mainstem and side channel habitats where near GOC water temperatures
exist for approximately seven months.Upwell ing exists in mainstem
VI-9
and side channel areas but its thermal value is significantly reduced
due to the large volumes of aoc water in these channels.Shorefast
and slush ice form along channel margins filling low-velocity areas,
where fi sh mi ght otherwi se overwinter,with ice.tvli d-channel
velocities generally exceed those considered suitable for over-
wintering habitat.In addition large volumes of anchor ice and a
thick ice cover (4-6 ft)form over mainstem and side channel habitats
(R&M 1983a).
Much of the main channel and side channel surface areas possess high
velocities and suspended sediment concentrations which are not
suitable for small fish (refer Table VI-2,Part D).In portions of
these habitats where streambed materials are large enough to provide
juvenile fish refuge from high velocities,interstitial spaces are
generally filled by densely packed glacial silts and sand,thereby
preventing fish from burrowing into the streambed.Rearing areas
associated with mainstem and side channel habitats are typically
located in low velocity areas along the shoreline margin,or in
backwater areas.Shoreline gradients are often mild,hence seasonal
variations of streamflow can cause large changes in wetted surface
area (Klinger-Kingsley 1985).
Jl..lthough turbidity has some value to juvenile chinook for cover
(Suchanek et al.1984)high turbidity also limits light penetration
and reduces primary production levels in mainstem and side channel
habitats.Low primary production levels result in a low aquatic food
base for rearing fish.Thus,turbidity has both beneficial and detri-
mental effects on rearing habitats in the middle Susitna River.Side
sloughs and side channels that fluctuate between clear and turbid
water habitats in response to streamflow variations,appear to provide
better conditions for primary and secondary production than areas that
remain turbid throughout'summer.While the area is clear,primary
production rates would be high,stimulating production of benthic
prey.Under higher turbidities,the young chinook could move into
these areas and feed without unduly exposing themselves to predation.
VI-10
-
-,
However,if these areas remain turbid continuously,aquatic food
production would likely be reduced.
The most important variables affecting fish habitat in the middle
Susitna River are streamflow,upwell ing,temperature,turbidity,and
suspended sediment.Streamflow and upwell ing are most influential for
determi ni ng habitat avail abil ity,where as temperature,suspended
sediment,and turbidity are the primary regulators of habitat quality.
The relative importance of these habitat variables changes with the
season,species,life stage and habitat type being considered.The
habitat index values (column totals)appearing in Table VI-2 are
listed in Table VI-3 to identify the evaluation periods and habitat
l~pes most limited by natural conditions.
Table VI-3.Summary of habitat and evaluation period indices for
the middle Susitna River as derived in Table VI-2.
-
Evaluation
Evaluation Side Side Upland Tributary Period 1
Peri od Mainstem Channel Slough Slough Mouth Index
Spawning -6 -3 +5 +1 +3 0
Incubation -9 -7 +7 +4 -2 -7
Overwintering -9 ",:9 +7 +3 +1 -7I
Summer Rearing -6 -4 +5 +2 0 -3
Habita t Index 2 -30 -23 +24 +10 +2
1 Row total
2 Column total
VI-ll
The information summarized in Table VI-3 reflects the detrimental
influences of high mainstem discharges and sediment concentrations
duri ng summer and of low streamflows and stream temperatures duri ng
winter.Review of the habitat-and evaluation period indices in
Table VI-3 indicate that the most stressful period of the year for
fish occurs during fall and winter.Naturally occurring physical
habitat conditions are least limiting to spawning and most limiting to
incubation and overwintering.It is also evident that mainstem and
side channel habitats are more adversely effected by the natural
streamflow,stream temperature and sediment regimes of the Susitna
River than are slough and tributary mouth habitats.
VI-12
-
-
-
-
-
-
.....
i
\
.-
Influence of Project Design and Operation on
Downstream Physical Processes and Fish Habitats
Construction and operation of the proposed Susitna Project would alter
the-natural streamflow,sediment,and thermal regimes of the mi ddl e
Susitna River.These changes would affect,to varying degrees,
i nstream hydraul ic conditi ons,turbi dity,ice processes,streambed
compo'sition,upwelling,and stream channel geometry,all of which
influence the availability and quality of fish habitat.Using this
opportunity to:(1)improve incubation and overwinter conditions,
(2)reduce high summer streamflows and sediment concentrations,and
(3)maintain or improve existing clearwater spawning and rearing
habitats appears to be a reasonable goal when establishing instream-
flow requirements for the middle Susitna River.However,attainment
of this goal depends upon understanding the degree of control alterna-
tive design and/or operation criteria might exert on downstream
physical processes and habitat variables.
Some project-induced changes,such as to the natural sediment and
turbidity regimes,are inherent with project construction and offer a
very limited opportunity to be influenced by project design or opera-
tion.Other project-induced changes,such as to the natural stream-
flow and.stream temperature regimes are also inherent,but these
changes may be moderated or controlled through project design or
operation.Understanding the degree of control project design and
operati on mi ght have over changes to natural processes and phys i ca 1
habitat variables can provide an effective means of developing
measures to avoid or minimize negative effects and maximize beneficial
effects project operation on downstream fish habitats.
Alternative design considerations and operating policies will afford
varying degrees of control over the natural streamflow,stream
temperature and sediment regimes of the river.Based on information
provided in Section IV and other project reports,the degree of
control over aquatic habitat variables afforded by alternative design
VI-13
----,-------_._--------~-~--------------------
or operating criteria can be ranked in ascending order of effective-
ness according to:(1)control over downstream sediment concen-
trations and turbidities,(2)control over the magnitude and
variability downstream temperatures and ice processes and (3)control
over downstream flow.Each of these topics are discussed separately
below.
Sediment and Turbidity
The 8.6 million acre-foot impoundment behind Watana dam will trap
the sand and larger sediments currently being transported from
upstream sources (R&M Consultants 1982d;Harza-Ebasco 1984e).Thi s
reduction in sediment load is expected to result in some degradation
of the main channel downstream from the reservoirs (Harza-Ebasco
1985e).A general coarsening of streambed materials should occur
within the middle Susitna River as sand and other fine sediments are
eroded from the streambed and transported downstream.
However,not all suspended sediment would settle out in Watana
Reservoir.Very fine sediments «~microns)are expected to remain
in suspension throughout the year,causing streamflows downstream of
Watana Reservoir to change from highly turbid in summer and clear in
winter to moderately-turbid throughout the year (Peratrovich et al.
1982;Harza-Ebasco 1984e).
Alternative design or operating criteria for Watana or Devil Canyon
Dams affords a very limited degree of control over downstream
suspended sediment concentrations and turbidities.Both these habitat
variables are far more influenced by reservoir size and retention
time.and particle size and light refraction than by the manner in
which the dams would be operated.The reduction in mid-summer
suspended sediment concentrations is expected to·have an
unquantifiable but beneficial influence on habitat conditions for
aquatic insects and immature fish.Both have been found to respond
favorably to reduced sediment transport rates in other systems (Bjornn
VI-14
""""
~,
'"""I
-
-
".,..
r-
I
-
et al.1977).At present,project-induced changes in natural tur-
bidity level s are not sufficiently understood to forecast the net
effect of project altered turbi diti es on food producti on and fi sh
habitat in the middle Susitna River.However,work is under way which
should improve the level of understanding by early 1986.
Temperature and Ice Processes
Downstream water temperature would be altered by impounding the
natural flow of the Susitna River.The reservoirs will attenuate the
annual variation in stream temperature by storing heat energy during
spring for redistribution during fall and winter.With-project
rna instem water temperatures are expected to be cool er duri ng summer
and warmer during fall and early winter.Mid summer and mid winter
stream temperatures are not expected to change appreciably from
natural (Univ.of Alaska,AEIDe 1984).Alternative multi level intake
designs and operating criteria can provide only a moderate degree of
control over ma i nstem water temperatures because of the overri di ng
influence of air temperature (APA 1984a).
Dewatering and freezing of streambeds and a prolonged period of near
zero degree water temperature appear to be the most critical habitat
conditi ons affecti ng natural fi sh popul ati ons in the mi ddl e Susitna
River (refer Table VI-2).An increase in mainstem water temperature
over natural stream temperatures during fall and early winter would
extend the period of biologic activity,delay the onset of winter ice
processes and possibly improve overwinter survival in the affected
habitats.Were water temperatures sufficient to prevent formation of
an ice cover,it is expected that terrestrial vegetation would become
better established along shorelines and on partially vegetated gravel
bars.This change would improve streambank stability and provide fish
Sireater access to streambank cover and terrestrial insects.Lack of
an ice cover would also preclude staging,thereby reducing the
frequency at which side slough habitats are overtopped during winter.
VI-15
Streamfl ow
Streamflow is the primary driving variable which either directly or
indirectly effects all aquatic habitat variables (Fig.VI-2).In the
middle Susitna River,different aspects of streamflow are important at
different times of the year and to different habitat types.Mai nstem
water surface elevations and site specific depths are of greatest
concern in side channel and slough areas where the highest degrees of
habitat utilization have been observed (ADF&G,Su Hydro 1983e).These
habitats are the most vulnerable to dewatering by abnormally low
summer streamflows (Kl i nger-Ki ngs 1ey 1985)or to overtoppi ng duri ng
winter because of abnormally high discharges and enhanced river ice
conditions (Harza-Ebasco 1985d).
Velocity appears to be of secondary or tertiary importance depending
upon the speci es and habitat type bei ng evaluated.Habitat response
curves (Section V)for both spawning and rearing fish in side slough
and side channel habitats are more significantly influenced by
increases in depth resulting from overtopping (a water surface
elevation phenomena),than by site specific velocity conditions.
Analyses of hydraulic conditions in shoreline margins of the mainstem
and large side channels (Williams 1985)indicate that flow velocity
often suppresses rearing conditions for juvenile salmon.Shoreline
margins are usually devoid of cover objects and stream channel and
streambank gradients are often too steep to provide any significant
change in the amount of wetted surface area possessing suitable
rearing velocities unless mainstem discharge was reduced to the range
of 5,000 cfs.
Project operation could prOVide a considerable degree of control over
the magnitude and variability of streamflows in the middle Susitna
River (Harza-Ebasco 19849).During the open water season,streamflow
could be regulated to provide relatively stable depths and velocities
in side channel and slough habitats,or could be intentionally
fluctuated during early summer to flush undesirable sediments from the
VI-16
-
-
")~--l )1 ~--1 )---)
LEGEND
<:......
I
I--'
'-.l
[Pioject Design and Operation {
>>>II --:::::!.
WATER
TEMPERATURE
Degree of==
Control
HIGHEST
~
LOWEST
Figure VI-2.Ranking of habitat component in accord with the degree of control project design
and operation might provide them.
streambed.Streamflow fluctuations during late summer and fall could
assist adult salmon gain access to side slough spawning habitats.
However,persistent cyclic fluctuations (such as those associated with
hydropower peaking)would likely be detrimental to fish and fish food
organisms in mainstem and side channel habitats.During winter,
higher than natural,but stable,streamflows would likely improve
habitat conditions in mainstem and side channel habitats presently
influenced by river ice or dewatering and freezing.Higher than
natural water flow would contribute to improved upwelling in the side
sloughs which would likely benefit incubation and overwintering
conditions.However,if mainstem water surface elevations associated
with hi gher wi nter streamflows were suffi ci ent to cause recurrent
mid-winter overtopping of slough habitats the inflow of cold mainstem
water would adversely affect incubation and overwintering conditions
in the side sloughs.
Fish Habitats
The relative degree of influence that with-project physical habitat
variables might exert on the suitability of aquatic habitats in the
middle Susitna River is summarized by Table VI-4.These subjective
index values are based upon the assumption that the with-project
physical habitat conditions implied by preceding discussions do occur:
sed iment transport rates a re expected to be si gnifi cantl y reduced,
turbidities decreased in summer and increased during winter,stream
temperatures increased during winter,and ice processes moderated
upstream from RM 125.In addition it is assumed that streamflows
would be in the range of 12,000 to 14,000 cfs during summer and 8,000
or 9,000 cfs during winter.
The index values in Table VI-4 may be used to evaluate the relative
degree of influence with-project physical habitat variables might
exert on each of the habitat types at different times of the year.
These indices do not reflect the important synergistic influence of
biologic processes on habitat quality and therefore,do not
VI-18
....
-
Table Vl.~4.Relative degrees 1 of influence that estimated with-project physical habitat variables
might have on the suitability of middle Susitna River habitat types during the four
evaluation periods.
Habitat*Side Side Upland Tributary
Variabll~Mainstem Channel Slough Slough Mouth
PART A:Spawning (August 12 -September 15)
Mainstern flow -1 +1 +1 0 +2
Upwelling +2 +3 +2 +2 +2
Substrate composition -1 +1 +1 -2 +2
Suspend(~d sedi ment 0 0 0 0 0
Turbidity 0 0 0 0 0
Water T(~mperature 0 0 0 0 0
Habi tat Index 0 +S +4 0 +6
PART B:Incubation (August 12 -March 24)
Mainstem flow +1 +1 +2 0 +1
Upwelling +1 +2 +3 +3 +1
Substrate composition -1 -1 +1 -1 +1
Suspend1ed sediment 0 0 0 0 0
Turbidity 0 0 0 0 0
Water t,emperature -1 -1 +2 +2 -1
,-Ice pro1cesses -1 -1 -1 0 -1
I Habitat Index -1 0 +7 +4 +1!
-
PART C:Overwintering (September 16 -May 19)
Mainstem flow +1 +1 +2 0 +1
Upwelling +1 +2 +2 +2 +1
Substrate composition +1 +2 +2 -1 +2
Suspended sediment 0 0 0 0 0
Turbidity +1 +1 0 0 0
Water temperature -1 -1 +2 +2 -1
Ice processes -1 -1 -1 -1 -1
Habitat Index +2 +4 +7 +2 +2
Mainstem flow
Upwelling
Substrate composition
Suspended sediment
Turbidity
Water temperature
Habitat Index
+2
o
+1
o
+2
o
+5
PART D:Summer Rearing (May 20 -September 15)
+2 +2 0
0 +1 +1
+1 +2 +1
0 0 0
+2 0 0
0 0 0
+5 +5 +2
+2
o
+2
oo
o
+4
-
Evaluation scale
+3 extremely beneficial
+2 moderately beneficial
+1 slightly beneficialonoeffect
-1 slightly detrimental
-2 moderately detrimental
-3 extremely detrimental
*Anticipated with-project conditions for the habitat type during the season evaluated based on
information contained in the draft license amendment (APA 1985a).
V1-19
___._.R_................--
necessarily define any particular increase or decrease in fish
populations.
However.were the proposed proj ect des i gned and opera ted with the
intent of ameliorating the more stressful naturally occurring physical
habitat conditions.a considerable degree of improvement appears to be
attainable in mainstem and side channel areas {Table VI-5}.Through
project-i nduced reducti ons of hi gh summer streamflows and sediment
transport rates.and an increase in wi nter streamflow and tempera-
tures.a considerable degree of improvement in both summer and winter
physical habitat conditions appears to be attainable.The successful
completion of IFR Volume 2 and the Comparisons Process will provide
the necessary technical information to define the most practical
streamflow and stream temperature regimes for attaining the beneficial
physical habitat conditions implied by the habitat and evaluation
period indices in Table VI-5.
Table VI-5.Comparison between habitat and evaluation peri od indices for natura I (N)
and with-project (P)conditions.-
Evaluation
Evaluation Side Side Upland Tributary Period 1
Peri ods Mainstem Channel Slough Slough Mouth Index ~
N P N P N P N P N P N P
Spawning -6 0 -3 +5 +5 +4 +1 0 +3 +6 0 +15 -i
Incubation -9 -1 -7 0 +7 +7 +4 +4 -2 +1 -7 +11
Overwi nter -9 +2 -9 +4 +7 +7 +3 +2 +1 +2 -7 +15
Summer Rearing -6 +5 -4 +5 +5 +5 +2 +2 0 +4 -3 +21
Index 2 +8 +2 +13 ~j
Habitat -30 +6 -23 +14 +24 +21 +10
Row total ~i
2 Column tot a1
-
VI-20
r
I
r
I,
r
,....
r
l
r
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VII-8
~,
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""'"
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VII-lO
-
""'"
"""
......
-
-
.....
1984e.Reservoir and river sedimentation.Final
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-
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--------..=------------."...._...,.,--------------------
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VII-12
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VII-17
----.._------------_.......--------------------------
1982a.Streambed material survey.
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VII-18
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1982 Susitna basin
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VII-19
--.......,--,-...--_........-------------------------------
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